Short answer is yes - TM on MyCloud (v1 anyway) over SMB works with BigSur provided you make some changes as I outlined in SOLVED: Tweaking Samba/SMB2 for Mac & Androids even with the old Samba 4.3.11 Most of the paramenters I highlighted in that post are default, but as a minimum you need these in BOTH smb-global.conf and tm_config.conf:
min protocol = SMB2
ea support = yes
vfs objects = catia fruit streams_xattr
I created a more generic post on the Samba wiki: Configure Samba to Work Better with Mac OS X - SambaWiki which has been reviewed by the Samba developers.
