Hopefully others will report their experiences as well, but the first 3 systems listed in my signature don't have this problem. I can connect both USB flash drives and SATA SSDs in external USB 3.0 enclosures without any sleep/wake issue.
Something that surprised me recently:
- I've installed Big Sur on a SATA SSD mounted in an external USB 3 enclosure.
- Big Sur will sleep and wake properly.
I recall this being a problem with Catalina, which would eject external drives during sleep. If macOS happened to be on an external disk, it would not reconnect and hence the system would not wake from sleep. I should add that this behavior [with Catalina] was observed using Clover, whereas Big Sur is (currently) bootable only with OpenCore.