There are 3 hidden gems in MacOS which are not widely known, and one (.nobackup) I recently discovered by myself. These allow more granular control over indexing, iCloud synching and Time Machine inclusion. I am not going to discuss here whether the syntax is clumsy, rather I am very glad that at least these exist. So here goes:
Any file or directory where the name contains “.nosync” is ignored by iCould synchronisation
Any file or directory where the name contains “.noindex” is ignored by Spotlight
Any file or directory where the name contains “.nobackup” is ignored by Time Machine.
Or not? Later: it may depend on the system version. Simon tells me that “.nobackup” works well in BigSur (thank you!).