proper format for external hard drive time machine

Time Machine took off and worked fine for the remainder of the day…until this morning when I saw the same notification again! “Time Machine failed because the drive is not formatted as Mac OS Extended format (Journaled) GUID.” I started Time Machine on one partition and copied other files into the second partition. So this time I erased the drive, partitioned it into two 2TB partitions, then formatted them both as Mac OS Extended format (Journaled) GUID. I found somewhere online that Time Machine may not work properly if there were any other files stored on the same drive with the Time Machine folder. The next morning I woke to find the same notification again. I plugged it back into the Mac and reformatted it to Mac OS Extended format (Journaled) GUID, set up Time Machine and away it went, working perfectly for the remainder of the day. I removed the disc, connected it to a Windows computer and reformatted it. Nothing I tried to get it working helped. I could not even reformat it using Disk Utility. I could not unmount the disk or eject it. I couldn’t think of any way that could happen, but believed its story. “The backup disk is not in Mac OS Extended (Journaled) format, which is required.” Then the next morning I had this notification: Time Machine continued to work fine all day. I then decided to use some of the space for external file storage and copied several GB of files to it from another drive. I first used the drive only for Time Machine and it worked fine for a couple days. I have a 4TB WD My Passport for Mac that I connect via USB primarily for Time Machine. I recently updated my Mid-2012 MacBook Pro directly to Catalina 10.15.5, skipping any earlier versions of Catalina. Thus far I haven’t found what the problem is. I have posted this issue on the Apple forums. I hope someone here has some helpful information for me. I have searched for posts with my specific issue but have not found any, here, or on Google.

Proper format for external hard drive time machine