The illusions and delusions of the world

In any situation like you describe, the often best thing to do (as a Buddhist or anyone) is to focus and develop your own personal and familial situation towards peace and concord.

Like you said, government is more of an idea not so much a tangible thing, made up of individuals. The way of change towards large groups is the way of change in the individual. If you can find some peace and happiness in your own life, then you can begin to spread it to others; and who knows how far those effects reach.

If you find you are obsessing over others and their actions, might be better to focus on making peace with those obsessions first; That is something tangible you can do about it.

The Theravada tradition has the concept of conventional truth and ultimate truth. You can read about it in this excellent answer.

It does not say that the universe is unreal. Rather, it differentiates what we sense from the six sense media, from the concepts that we create in our mind through reification (papanca).

Although the Buddha himself was fully enlightened and saw things exactly as they are, and did not cling to concocted concepts, yet he made use of concepts as far as they were useful. He did not cling to them but saw them as mere conventions. After all, are not the Buddha, the Dhamma and the Sangha all mere concepts?

The monastic rules of the Vinaya has rules pertaining to food, lodging, medicine, conduct etc. There are rules pertaining to medical care. The Buddha ate, slept, wore robes, took medicine when he was ill etc.

The Middle Way of the Buddha avoids both extreme indulgence and extreme asceticism. It includes moderation in food, healthcare and living. To neglect healthcare is to go against the Middle Way of moderation.

From Kucchivikara-vatthu of the Vinaya, the Buddha taught:

"A sick person endowed with five qualities is hard to tend to: he does what is not amenable to his cure; he does not know the proper amount in things amenable to his cure; he does not take his medicine; he does not tell his symptoms, as they actually are present, to the nurse desiring his welfare, saying that they are worse when they are worse, improving when they are improving, or remaining the same when they are remaining the same; and he is not the type who can endure bodily feelings that are painful, fierce, sharp, wracking, repellent, disagreeable, life-threatening. A sick person endowed with these five qualities is hard to tend to.

"A sick person endowed with five qualities is easy to tend to: he does what is amenable to his cure; he knows the proper amount in things amenable to his cure; he takes his medicine; he tells his symptoms, as they actually are present, to the nurse desiring his welfare, saying that they are worse when they are worse, improving when they are improving, or remaining the same when they are remaining the same; and he is the type who can endure bodily feelings that are painful, fierce, sharp, wracking, repellent, disagreeable, life-threatening. A sick person endowed with these five qualities is easy to tend to.

Based on this Vinaya quote, I would say that the Buddha himself would have wanted his followers to practice moderation, and accept the advice of healthcare professionals and the government when dealing with the Covid-19 pandemic.

Also, spreading misinformation about Covid-19, masks and vaccines is against the fourth precept of not speaking falsehood.

Wearing a surgical mask is more for the wearer to avoid spreading pathogens to others, than for the wearer's own protection from contracting an infectious disease. As such, wearing a mask with the explicit intention of reducing others' suffering, is also an expression of compassion (karuna).

The quote from DN 26 below, also shows that the Buddha did not promote anarchy. He stated that the wheel-turning monarch should provide just protection and security to his subjects and also care for their welfare.

‘But sire, what are the noble duties of a wheel-turning monarch?’

‘Well then, my dear, relying only on principle—honoring, respecting, and venerating principle, having principle as your flag, banner, and authority — provide just protection and security for your court, troops, aristocrats, vassals, brahmins and householders, people of town and country, ascetics and brahmins, beasts and birds. Do not let injustice prevail in the realm. Pay money to the penniless in the realm.

I would even say that a responsible Buddhist should support his or her government and follow its advice, if the government is discernibly doing the right thing, and if its advice is in accordance with the five precepts, Right Action, Right Speech and Right Livelihood. For e.g. conscription into military service is against Right Livelihood.

For example, government is an idea and a fabrication, it is not a person or a thing, it just a group of individuals. A lot of people believe in this idea and accept it as something real

I heard a nice analogy once. If you have a dog and tell it to "come", then it either comes or it ignores you: but if it ignores you, at least it can hear you, and you're being ignored by "the whole dog".

Compare that to a bureaucracy -- if you tell a bureaucrat or functionary something and then nothing happens, that doesn't even mean that the "whole bureaucracy" has necessarily "heard" you.

So in that sense it's true that the government isn't a "thing" -- in the sense that you can't touch it, you can't talk to (all of) it on the phone. That doesn't mean that the government "doesn't exist" though: I tend to equate "non-existent government" with "failed state" -- https://en.wikipedia.org/wiki/Failed_state for example Somalia -- if hopefully you're living in a society that's better organised and less violent than that, perhaps that's evidence of some at least partially-effective government.

they believe it so much they follow without thinking

Maybe you should follow it sometimes, but with thinking.

Following government orders without thinking is a characteristic of Totalitarianism, and historical problems including genocide etc.

But mask-wearing for example is recommended by government and by health professionals for a purpose -- which is that it's to avoid harming (infecting) other people. And that seems to be a worthwhile motive, which is inline with Buddhist ethics.

And it's not only the motive (i.e. being harmless) but also the mechanism (wearing masks) that seems to me sensible -- believable -- surgeons for example wear surgical masks, to avoid infecting their patients. Wearing masks, using vaccines, fits with everything I've ever learned (at school and afterwards) about the history of medicine and science and epidemiology and so on.

How do we stay on the path, when our actions of not following these illusions makes a target, by not wearing masks, taking vaccines and not following government illusions?

I think it's a matter of doing things "wisely".

If "the government" (or anyone else) tells you to do things which harm others, perhaps that's advice which you should happily ignore.

If it's advice on how to protect others from harm, perhaps that's advice which you should happily hear.

Your argument seems to be ... "1) This advice comes from the government. 2) The government doesn't exist. 3) Therefore I should ignore the advice." -- which doesn't seem to me a sensible argument.

I gather from the suttas that an argument like, "Nothing exists" is a kind of wrong view, an extreme.

And I think that even the Vinaya implies some obedience to, living with, the national laws (or "king's laws"), and performing bodily actions which protect others from harm (and even which protect yourself from ill-repute).