I often forget the brushes and Mypaint brush settings I use in a picture, like the color pallets tab, adding a custom brush set tab would enable itemizing brushes into groups, making re-finding previous brush settings and selections and easy.
Don’t know if they have covered that here but they have in Gimp Chat and you can put all of your brushes in category folders, You could even make a folder of brushes you use the most.
I’ll see if I can find a link for you to see.
Can’t find it but I think you can do htis with all of your resources in Gimp. There is a thing called a resource manager. Maybe you will find it if you google for it.
With your brushes if you make folders within your brushes folder, of the different types and then move the different types into those folders. You will just have to then search in your brush dialogue for the type you want and only those brushes will show.
Don’t know if you can do this with MyPaint brushes
You may also want this
https://gimp-tools.sourceforge.net/managementtools.shtml
If you want to keep the settings, edit the brushes (if you can), if not copy, then edit, saving the edited brushes as you normally use them; ie size, spacing, dynamics etc. Then give these a specific name which you can then put these into your custom folder.