https://daniel.haxx.se/blog/2022/05/12/a-tale-of-a-trailing-...
THE money quote :
The trailing dot then means the name is to be used actually exactly only like that, it is specified in full, while the name without a trailing dot can be tried with a domain name appended to it. Or even a list of domain names, until one resolves. This makes people want to use a trailing dot at times, to avoid that domain test."