iPhone XI won't backup to iMac

Hi there, I have no idea what to do.

Since a couple of weeks (I can't see what would the exact trigger be), my iPhone refuses to back up to my iMac (running latest OS version).

I erased all previous back up (from Finder). I restarted my iMac many times.

Every time I connect my iPhone with USB cable and hit the "Backup" button in the Finder, I get this error : "iPhone can't back up, because an error occured." Sorry for the bad translation.

I don't want to synch to iCloud because I don't want to lose all my Health data.

Any idea ?

Thanks in advance.

M.