Vlad I installed Firefox Focus and the result is the same. Of course on this version of iOS all browsers are just wrappers around Safari’s engine, but this seems to rule out browser specific quirks. Not sure whether you’re aware that because I can no longer upgrade iOS, I can’t get a newer version of Safari’s engine.
There seems to be a non-backwards-compatible framework or API that is really popular these days because while I can still browse e.g. YouTube, a lot of websites increasingly fail to render. Even GitHub.
The last update, 12.5.7,[2] was released on January 23, 2023.
It’s apparently just a year old! I’d get a new iPad but life is expensive these days.