I have a similar problem, large monorepo, things have become really bad lately to the point that the cursor is unresponsive. The only workaround I have found is opening each folder of the monorepo in its own IDE instance

Feel this so hard. The opposite is also true where you have a micro-service architecture and cursor faceplants in workspaces with multiple repos. We ended up building cortex.build partly because of this exact pain. Our context engine builds a git-aware dependency/provenance graph so it can stay local and only pull the relevant slice across a massive repo or dozens of smaller ones.