The way I managed to limit charging limit on my Ampera-e (European Bolt) was to configure "only charge when low price". Knowing the charge rate you limit the number of hours to charge, and you do not charge before you reach 50%. On a daily basis I charge two hours at night with 7.3 kW, which is enough for my job-commuting, and only if I am close to 50%. This results in fill-rate alternating between 50 and 70 %. For long distance drive I just override time scheduled charging with immediate charging in order to fill it to 100%.
Not an ideal solution, but it works.
As a programmer, I would guess that GM could solve this "max charge problem" with 8 hours of programming. I think GM has a lot to learn from Tesla which listens to their customers in community forums and solves problems quickly.