Do they still not require ID when you buy a SIM card in Ukraine?

You can just grab any prepaid SIM and use it if that's your style

That said, such high-tech operation is just a geeks fantasy about spies. When you cross the line where it becomes reality, you’re either a very big name with a sudden drug/rape history or a subject for waterboarding which is the most effective cryptoanalysis tool invented.

Yes, burner sims definitely help evade investigations, but they are harder to get nowadays, depending on jurisdiction. For instance you can't pay cash for a SIM in North America. It has to be a credit card or a bank transfer and that's a form of ID.

I was using telegram for one single usage, which was a group organizing local meetups events for expats. When I switched smartphone I really didn't want to install an app just for one group and would have preferred using telegram web to consult it occasionnally. Every time I tried logging in on a computer/smartphone it told me to validate the login from telegram on my original, now wiped clean, smartphone. I just gave up.

Then why is a phone number needed to register? If PII is "not shown to anyone in any way" then it should be completely unecessary to provide it to the service. Do not let that particular wool be pulled over your eyes.