could not unmount disk external hard drive time machine

Kind of hard to do when they don't even show up on my desktop.Changes to macOS and Disk Utility in macOS 10.15 Catalina now make this older method obsolete. They just kept them and didn't specify exactly why, just generally that they had been tampered or altered. I did as their tech department instructed, sent them back for replacements.

Other than that, I don't see where I went wrong. so I didn't buy the warranty, where I could have just taken them back to the store. I didn't do this because my dad used to sell them and he knew how often they were actually used, that it isn't worth the money's and the fact that so many past drives always work. What I did wrong? I didn't buy the warranties. Of course, there's nothing new on the status according to the support page. I finally emailed them again (polite) explaining this all again, and asked for at least a timetable on an answer, and was told to expect one this past Monday. That was bumped up to a Level 2 Technician, and nothing happened with this for about ten more days. So, I've had a phone call with support, and a chat with online support who told me to email the department who told me that they weren't going to replace them. They didn't even specify exactly what was wrong with them. I get an email telling me they've been tampered with (modified, something like that) and that I will be receiving no replacements, nothing. Two weeks go by, there's no update on the RMA page even though USPS had confirmed delivery. So, I take the time and effort to box them up very well, drive to the post office and pay forty bucks to send them away. I contact Western Digital, they tell me to send them back for replacements. as this isn't my first rodeo with this kind of thing. I tried a different computer, different cables, power supplies, safe start, etc. One can be seen with the Western Digital software tools, but in reformatting it, the drive just stalls for hours. So, I had to go to two different stores because no single store had two of these drives. I do this every year-and-a-half to two years, and the previous drives go into secure storage. I'm a bit gun-shy about external hard drives right now because I (here's a story) watched the ads for weeks, then went to OfficeMax/Depot and purchased two Western Digital 10TB hard drives. Thanks a lot! You've saved me a lot of time in troubleshooting.

Could not unmount disk external hard drive time machine