clean every material that is not in use (select all material at the material palette, right click and Delete. Calm, it only erases the unused materials)
repeat the previous step (you may have to save and reopen the file) many times
clean every geometry that is not in use
pay attention to the large assets you have entered, especially QuixelMegaescans and your own assets (you can see how large they are in the userlibrary and Quixel downloaded items directories)
Twinmotion vegetation is not big, but the imported ones may be