I have the same problem (PS5), and, sadly, cannot help you. This issue is reported two times through the issue tracker (one expired) and I've replied to both issues, this is the last one:
https://issues.frontierstore.net/issue-detail/59703 ("Game crashes even on perfect computer as per requirements"). I had this issue occur on the Germany square map and the Biosyn square map (didn't try any other square maps because I assume the issue is there to). Rebuilding database, clear cache, reïnstalled the game etc. Nothing works. I also have a park with all dino's from all DLC's, all attractions and builings from all era's except Malta, on a regular Biosyn sandbox, and there the issue doesn't occur. This is strange because this park would be much heavier to load than my Biosyn (or Germany) square map which doesn't have any dino's yet.
I save very often, so I could revert to a previous save and tried many things. But when I load previous saves, everytime I build more, i cannot load the save after exiting, so I'm also stuck. I've tried everything I could think of, deleting all powerlines and turing the infinite power setting on, deleating all rangers and MVU's, deleting all Matla buildings, deleting all buildings on the edge of the map etc, but nothing works. Except when I was decorating one area for a long time. So I sayed in one spot for a long time and didn't move around the map. Then I was able to load the file after exiting. Also strange; I was able to add a lot of decorations, trees etc in one spot, but I am not able to ad ranger stations to the enclosures (when I do that, the game again crashes during loading).
Screenshots of the Biosyn square map from the save I could still load (but couldn'd add anything without not being able to load the save after exiting):
For comparison, screenshots from the regular Biosyn sandbox map (with no crashes during loading):
