What do Buddhists think of leather?

Afaik there is an allowance to use leather sandals but there is also a restriction on the thickness of the soles. Maybe someone can confirm with a vinaya reference.

A bhikkhu in the middle Ganges Valley may wear new leather sandals only if the soles are made from a single layer of leather. He may wear multi-layer sandals if they are cast-off, which according to the Commentary means that they have been worn (presumably, by someone else) at least once. Outside of the middle Ganges Valley, one may wear multi-layer sandals even if they are new. https://www.dhammatalks.org/vinaya/bmc/Section0042.html

Buddhism is not a place where giving permission to do things and prohibiting to do things. All it explains it is if you do this what would be the result in return plus it explains the whole world up to a greater extent.

To answer your question, If you take that vegetarian goes with buddhism no it is not. But killing animals is giving a bad result in return, it can be instantly or in later birth. About the leather, again it is the same. You can use the leather without attaching to that, without wanting to kill animals and collecting leather.

If your problem is that you can't use the cars with leather seats. Because that makes you feel bad as it is not align with buddhism, no you are wrong. As I said earlier it's not about using the things, it's about attaching to things. Attachment is the core problem explained in Buddhism. But again if you kill you will get bad results, so don't think that you can kill without attaching :) Because thoughts in the mind is what matters, not what we do.

Although Buddhism does not per se advocate for vegeterianism or even veganism, to help the practise of kindness & compassion it might helpful to go full vegan.

Why follow the diet the Buddha used to eat 2500+ years? It makes no sense because most people live in a somewhat modern city with access to supermarkets, where we can literally choose the more compassionate food choice.

We can literally prevent one more massacre with that vegan meal at the dinner table.

There are plenty objections why, from a moral perspective, vegeterian might not be enough. It's a good step in the direct direction, but the dairy & egg industry are inherently cruel.

The suttas do not explicitly forbid the use of animal products, but you must ask yourself how that animal felt during the process, which is in essence an empathy practise right there.

As far as as practicality of life is seen,
1.) Vegetarian food, now days is obtained by killing certain animal species but it is done unintentionally by farmer so no killing percept is preserved. I have even seen some farmers who remain sad, some even remorse for this doing.
2.) Even if vegetarian food involves killing, vegetables(other than garlic, onion) don't induce so much foil smell and don't generate so much heat within body like non-veg. do.
3.) When someone's livelihood is dependent on 'killing and selling animals', it increases too much killing instincts ... not good for someone aspiring to establish on dhamma.
4.) Others who buy leather or killed animals, simply help the killers in increasing killing instincts.

Conclusion:: Buying Leather or killed animals is not allowed.
Event:: If it is not allowed, then what about those seeking alms and allowing anyone to give meat of killed animal or human.
Conclusion:: They are simply encouraging anyone to directly or indirectly break no killing percept.

Not all Buddhists are vegetarian and the Buddha ate meat at times. Owning or buying leather is not prohibited. There are very good reasons to become vegetarian and abstain from eating meat or owning leather, but neither of these alone will lead to enlightenment. In other words, there are saints that ate meet and owned leather and there are very violent and awful beings who were vegetarian and never owned leather.

In the suttas, one finds simple directions such as this:

DN33:2.1.27: A mendicant with defilements ended can’t deliberately take the life of a living creature, take something with the intention to steal, have sex, tell a deliberate lie, or store up goods for their own enjoyment like they did as a lay person.

As you notice, there isn't anything about being a vegetarian or using leather. Those are details. Looking more carefully at the suttas themselves, we see that deliberately taking life is not acceptable. Therefore, if one finds a dead animal in a forest, eats it and makes leather, that is not deliberately taking the life of a living creature.

In modern society, that link between meat and leather is indirect. Others kill so that we may have meat and leather. When we buy meat and leather, we promote such practices, becoming complicit in the killing. Yet now we have oddities such as the Impossible Burger, which does not require the killing of a meat animal.

Not killing introduces us to love and compassion. Indeed, with limitless love and compassion, we simply cannot deliberately kill.

Practicing love and compassion is a start. For example, at the start of AN8.63, we see:

AN8.63:2.2: ‘I will develop the heart’s release by love. I’ll cultivate it, make it my vehicle and my basis, keep it up, consolidate it, and properly implement it.’ That’s how you should train.

Study the suttas and don't get caught up in rules and observances. We have robots for that--they are programmed to mindlessly follow rules. Instead, open your heart to loving kindness and compassion and more. Study the suttas and decide for yourself each moment what Right Action results from Right View. Use the precepts to guide your awareness of what needs to be done moment by moment. This is why the precepts are non-specific. The precepts encourage us to be mindful.

Monks can use meat/leather, if it is coming from an animal who died naturally(without intervention of human or trained animals, for them). It's just that they need to enquire first about the meat/leather being received.

Vinaya has given monks choice, story goes like....... "when devdutta enforced for vegetarianism........ buddha allowed monks to have choice of food but they must meditate hard and enquire about human meat".

Personally, as per choice given by buddha in vinaya, I reject non-veg./leather for good reasons.

Buddhists here (one) think that natural leather is not encouraged but can be tolerated out of necessity.