I'm sorry to hear about your troubles. Going by the specs listed in your signature, it sounds like the 5-bay USB enclosure isn't playing nice with the Pi4. Or one or more of your disks are actually on the brink of dying, causing OMV to automatically remount the filesystems on said disks as read-only in an attempt to prevent damage to existing data.
These are just a couple of possible reasons I can think of; a lot of people use USB drives as permanent shares but that's just not for me - give me native SATA any day of the week. (I'm running both a custom-built Intel server PC and an ODROID-HC4 - no USB whatsoever.)