Should I tell the truth in the visa interview?

Tell the truth.

Is it a good idea to the tell the truth?

Yes it is — always. Never lie, and never lie by omission either, by hiding details that you know are relevant to the situation.

Immigration officers are trained professionals who, by law, have to assume that foreign nationals have immigrant intent until they can show otherwise. They will immediately spot any cracks in your story and start digging, and any lies, however small, will instantly invalidate your credibility.

What is the purpose of your visit?

On top of that, you seem to be conflating purpose and timing. If they want to know why you want to go to the USA, "I want to be able to go whenever I want" is not an answer to the why, but the when.

You want to be able to go whenever you want – that’s fine, why? What are you going to do once you’re in the US?
Are there places that you want to visit as a tourist? Are you planning to work illegally on your tourist visa? Are you planning to overstay? Do you have enough ties to your home country that you’re actually likely to go back before your visa expires? Do you have any friends or family members who already live in the US, that could potentially help you overstay?
Can you afford to live in the US for the duration of your planned stay (i.e., do you have enough money to support yourself)?

Also, definitely tell the truth, but if I may, adopt a more agreeable delivery: I don’t feel like "I want to go wherever I want whenever I want" is an answer likely to be well received. It sounds defiant; I recommend that you avoid any behaviour or words which might be interpreted as defiant, arrogant or otherwise disrespectful or entitled.
For instance, you can say that because of the long wait times for interviews, the unpredictability of the worldwide Covid situation, etc, it is hard for you to schedule precise dates for traveling, but if at all possible, you would like to be ready to travel on short notice. You like to be prepared and have everything ready.

When going for an immigration interview, please remember at all times that you have no right whatsoever to enter the country you want to enter; an immigration officer has almost absolute power over the decision to grant you a visa, and if you lie (and they will catch you lying), they will probably do whatever they can to make sure that it’s hard or impossible for you to try again.

Always tell the truth in Visa interviews and similar meetings.
There are serious penalties for not doing so.

However, you should treat a Visa interview just like you would treat testifying in court (whether for yourself, or for/against someone else):

• Answer the question — fully but minimally — and nothing else.
• Do not volunteer excess information!

In your case, what parts are the necessary truth, and what parts are in excess?

Necessary Truths

1. You plan on visiting the US in the future for tourist reasons.
2. You do not know exactly when you will actually visit.
3. You can make a (very) rough guess of when you might be visiting.

Excess Information

1. "I want to be able to just decide on the spur of the moment." This answers a question the interviewer hasn’t asked: "why don’t you know exactly when you’ll visit?"
   — Even if you are asked that question, you should provide mechanism not motive. An example: "My work schedule and my other obligations are generally variable, as are my finances to a certain degree. I plan to visit in the second quarter of 2024. However, if I have an important or time-critical contract of work during that time, I may need to postpone. If I were to have a windfall project in 2023, I might want to visit a little earlier."

2. "…I don’t want to go to US this or next year…" They don’t want to know what you don’t want. (Personally, I never want to go to jail, but that’s not what I would lead with in a police interview, for what should be obvious reasons!) Answer only the questions asked.

3. "I don’t want to have to wait for 1.5 years for an appointment…" Nobody does. Again, don’t provide negatives.

4. Note also that the interviewer probably won’t ask: "What’s your motivation in applying when you’re applying?" Or "what is your attitude about travel?"

It occurs to me part of the problem is the meaning of the word "want."
The interviewer is trying to determine what you might or might not do once you arrive in country. They are asking "purpose of [proposed] visit."

If the interviewer wants more details, they will ask. If they ask, provide those details, but again, only answer the question asked, and give the minimum truthful answer.

A common technique used by ANY kind of "screener" (Visa interviewers, job interviewers, police, security, verbal academic boards) is to ask very open-ended questions and then allow the interviewee to shoot themselves in the foot with them. I have experienced this directly and personally during academic boards. One can uncover a LOT of information from an unwary participant just by letting them lead the interviewer by answering a chain of loose, unspecific questions. Attorneys (barristers) do the same in court.

REMEMEBER: It is not dishonest to limit your answers, as long as you are not leaving out pertinent, material facts. (Those are "lies by omission.") You are simply restricting the conversation to only what’s necessary to determine if you will be granted a Visa.

I spend my year in multiple countries as a tourist

This is a normal thing by now. We even have a question about Where can I travel for prolonged periods of time while legally working remotely for a company in my home country? and post covid we are seeing a lot of countries implementing one year "digital nomad" visas. I have been digital nomading in 2006-2008 and back then it was much less normal but now? this is fine. Just tell them the truth that you are digital nomading perhaps offer the same explanation you did for us just in case and that you want to include USA in your future trips. There’s nothing wrong with this.

You should always tell the truth! Especially in visa interviews, if they catch you lying there might be consequences on top of the refusal, which is pretty much the worst that can happen if you tell the truth.

If you have also waited ~1,5 years for your interview:

1. It doesn’t make sense calling it a chore you just want to get done
2. It strengthens the argument for applying without concrete plans

If you haven’t waited ~1,5 years for your interview: What makes you think it’s not just a temporary thing that the wait is so long (the employees might be busy with other things – e.g. covid has brought several new tasks)

Specifying a year (and season) is probably a good idea though.

Should I tell the truth in the visa interview?

The answer is: Yes.

In the "Intended Date of Arrival" field, select a date in 2023. That’s perfectly fine. In fact, in the comments for this field it says:

If you are unsure of your travel plans, please provide an estimate.

Tell them the same during the interview, if they asked. It is that simple.

Here’s a screenshot of the field: