There are ads in the form of product placement or company logos of sponsors.

Found this website in another post https://privacytests.org/

Self-hosting has other drawbacks. Your need to maintain your server, you need a steady internet connection and a steady power supply. These are things providers like Proton and Tuta deal with for you.

Does not answer your question but I just checked and you cannot customize the font in Mlem

Mlem for iOS let‘s you filter for keywords

Wow…