Please define "dirtier". I'm fairly sure that bacteria is on just about everything on earth. I'm made up of several pounds of bacteria right now... and this is not just normal but healthy.

If a toilet seat is covered with e.coli, monkeypox and streptococcus... I'm going to be more concerned about that than how many of them there are. The type of microcritters you are likely dealing with... matters.

Lastly... I don't know anyone who has fallen ill from using a keyboard. Or for going to the toilet, for that matter. Unless you are immune-compromised, and you don't engage in basic hygiene... you are probably going to be fine.