Is Simultaneous Big Sur Upgrade Necessary on All Macs Signed In With One AppleID?

My question is about the possibility that upgrading one of my two Macs (used for less critical work) to Big Sur while leaving the other (more critical Mac) on Catalina for a while longer. Some previous MacOS upgrades affected one or more Services that use iCloud for sharing/syncing (e.g., Messages, Keychain, Mail, Photos, Contacts, Calendars, Reminders, Safari bookmarks, Notes, Home).

I need to make sure that if I upgrade the less critical Mac to Big Sur that it won't affect any of the iCloud related services mentioned above in a way that would force me to upgrade my more critical Mac in order to restore its ability to continue using all those services.

I hope this question can be answered with some certainty.