Thank you JuergenAuer - you’re right - it is the webserver Apache that caused it. I have confirmation from my hosting provider who claims DNS verification is the only manual option for now.
Good point, yes Apache allowed creation of such folder starting with “.”.
It seems that either hosting provider simply wants to force people to buy far more expensive plans with automatically renewed Let’s Encrypt certs or it is tricky for Apache to make such URL’s containing folders starting with “.” work.