Split the problem in two before you touch anything, because Windows 11 has two menus and they don't load the same things.
The short menu surfaces commands from apps that register them the modern, packaged way. Old-style COM verbs - the ones every installer has been dumping into the shell for twenty years - get pushed down under "Show more options". So:
- if only "Show more options" is slow, you're paying for legacy handlers and there will be a lot of them
- if the first menu is slow too, look harder at the item you're right-clicking than at your extension list
Then vary the target rather than the machine. Right-click a file in a plain local folder, then one inside a cloud-synced folder, then one on a mapped network drive. A sync provider or a half-dead mapped drive will stall the menu while the shell asks about status, and that has nothing to do with extensions at all. A mapped drive pointing at something that no longer exists is the classic: it blocks for the full SMB timeout, every single time.
You already said desktop is fastest and normal folders are slower, which reads more like per-item work than a global handler.