OSX will use all of your RAM - you cant change that (Hip hip Hoorary!!). Memory management is superior to OS9. If ArchiCAD goes to the background it will release Memory for other Programs.
The only thing you can do is GET more RAM
Cheers John
John Hyland : ARINA : www.arina.biz
User ver 4 to 12 - Jumped to v22 - so many options and settings!!!
OSX 10.15.6 [Catalina] : Archicad 22 : 15" MacBook Pro 2019 [/size]