I've been working on a homebrew subbclass and when I tried to increase the ability score and the ability score maximum for one of the subclass features, the results didn't apply. After some searching on the internet and finding some threads with the same problems, I ran into a wall. Following MellieDM's example on this thread: https://www.dndbeyond.com/forums/d-d-beyond-general/bugs-support/21560-homebrew-ability-score-increase should have solved my problems. Unfortunately I did not reach the same outcome.

There is a slight possibility that the thread is already outdated in which case there might be another solution. There is also the easy solution where I adjust my ability scores manually when I reach the required level, but since it was an issue for me, it might be an issue for others. If it is a bug, I would like to report it.

I would add some screenshots, but it seems like I can't get that to work either.

Whenever I have tried to do what you are, the way it has always worked for me is like this:

Say you want to increase both a Characters Strength Score, and Maximum Strength Score by 2. I use a combination of 2 modifiers.
Modifier—>Stacking Bonus; Modifier Subtype—>Strength Score; Fixed Value—>2
Modifier—>Bonus; Modifier Subtype—>Ability Score Maximum; Primary Stat—>Str; Fixed Value—>2

The “Ability Score Maximum” is what will allow that score to go above 20. The “Stacking Bonus” is what will actually take it above 20. If that doesn’t work, I don’t know what to tell you.

That seemed to have fix the issue.

Thanks a lot!

Happy to help