I've seen a lot of interesting discussion regarding Mint's choice to downgrade some apps to the GTK3 version, later fork them. Whilst a lot of people have been critical let me provide another perspective
Projects like Mint do not like the state of GNOME/where it is going, instead of just sitting around whining about how much they don't like it they've taken it upon themselves to fork tools and maintain them for their own project. You may disagree with that choice but this is the spirit of FOSS
The same can be said about COSMIC from System76, they have had serious disagreements with the direction of the project so they said "fuck it, we're just going to build our own desktop and run it the way that we want to run it".
Could problems just be resolved upstream, maybe. But they have decided that this time has passed, any attempts made didn't go the way they wanted so they've decided to go off and do their own thing.