I would like to add a points counter similar to HP or Temp HP. It is NOT related in any way to proficiency bonus, ability bonuses, class level, or anything else determined by the character alone. And it needs to scale pretty high, so just making a bunch of checkboxes to click one by one won't work well. Is there any way I can implement this? Also, if there's an easy way to reset it to 0 as well, that'd be neat, but not necessary.

For a more fleshed out idea of what this UI problem I am trying to solve: this will be part of a feature that gains points based on creatures dropped to 0. Different creatures will grant different amounts of points based on size. When the duration ends, the points will be reset back to 0.

Yes. Create an Action, and set the number of uses to anything you want at each level. Please see the Homebrew Subclasses & Species FAQ #4 for additional information: (https://www.dndbeyond.com/forums/dungeons-dragons-discussion/homebrew-house-rules/131411-a-homebrewers-how-to-faq). Once the number is high enough, I think 10 or higher, it switches from boxes to a counter.

As for automatically resetting to 0, that’s not possible.

Thanks! I did read through that section of the FAQ, I just didn't realize that it would switch from the checkboxes to a counter. However, it also looks like the counter starts maxed out. It's not a huge deal, but is there any way to get it to start at 0? Also for posterity: you can click and hold a counter + or - button and then hold enter to repeatedly increment or decrement the counter.

No, there’s no way to get it to start at 0. It’s intended to count down uses, not up.

You should also be able to click on the number in the window of the counter and just enter the desired number instead of fiddling with the +/− signs.

Ah, gotcha. Thanks!