Alright, so from that we know that the MySQL issue is just unrelated broken packaging on your server. It can be ignored for the context of Certbot.
One trick that can work to track down which dependency is preventing a package from being installed is trying to install each dependent package that it complains about, directly. e.g.
apt install python3-certbot
and then if it complains about another dependency, try that one.
A different approach could be to forget about the PPA entirely, if you have insurmountable package problems on your server, and try use the portable certbot-auto instead.