Forgejo v9.0, which we'll (hopefully!) start using in a few hours, ships with a new quota feature for public and shared Forgejo instances!
We explained what this change will mean for you, the user (as well as some background information), in a new announcement titled "More power for you - what a storage quota will bring".
https://blog.codeberg.org/more-power-for-you-what-a-storage-quota-will-bring.html
TL;DR: We'll eventually starting enforcing a quota to curb abuse (e.g. people creating repositories full of empty commits taking up more than a GB), nothing drastic will happen immediately, and you will be able to request more space if you do need it.
Don't panic, everything will be fine!
(Feel free to ask us questions if you have any.)