Ah, that's the issue... yes, GMS2 currently has that hard limit, and I'll be honest and say that I'm a bit loath to mess with the code to work around it right now, as the 2.3.0 update is about to drop and it actually removed this limit completely from arrays. So, I'd prefer to wait a couple of weeks until that update comes out and then update the asset (as I'm sure the update will break something :( )... sorry if that's inconvenient for you, but I really would prefer not to spend days working on something that I'll probably need to re-do again anyway a few days later. Hope you understand and thanks for the purchase and reaching out!
BigNum, Instance Pooling, and Vectors, to the rescue!
- https://sahaun.itch.io/bignumgml
- https://derjulien.itch.io/gms2-vectors
- https://destrovel.itch.io/gamemaker-instance-pooling
You can also probably look into Adaptive Mesh Refinement.