I have a mostly simple solution, but it most definitely is a workaround. I used to have a shopping cart concept app several years ago that pretty much did the exact same thing you are trying to do. Item quantities were incremented within the item rows themselves. A single button click would “reset” all item quantity values in one shot with a little smoke and mirrors.
People usually get upset when I offer workarounds in their feature requests, so I’ll leave it up to you if you are interested or not. Maybe you’ve come across my method in other posts.
While I do agree with your request and would love to see it happen, it’s been a long standing request of Glide since the beginning. Ability to "Set columns", "Increment" and "Delete Rows" via multiple relations There are times when I just cannot wait for a feature requests to come to fruition, so I have to settle for a NOW solution.