Do the drives mount faster/normal if you connect/turn them on after your Mac boots?
I cannot find the article again at the moment. However, I read something months ago that Apple Silicon boot security would block external drives.* I think, I came across the article following attempts to figure out why my external drive (bus powered but always switched on) would not show up at all — I thought it was maybe dead. So, now I turn the drive off after powering down my Mac, then turn the drive back on after boot and login.
I do also vaguely recall reading something about this behavior changing after updating/upgrading to newer macOS versions. However, perhaps Apple Silicon boot security is causing a delay as it possibly ignores the drives until login.
* The only results I am seeing are for booting from an external drive. But the restriction I am speaking of is not relevant to whether an OS is installed on the external or not.