The vaccine hasn't stopped spread in rich countries, why would it do so in poor countries?
Also there haven't been enough variants as to determine that most variants are coming from poor countries. Speaking of delta, India has more population than the entirety of Europe. Mathematically it makes sense than a variant could come from there regardless of whether the vaccine does anything.
The problem here is not that Telegram disallows you from taking screenshots but that the OS, which should be on the side of the user, allows apps to disallow you from taking screenshots.