Upgraded to Big sur now I have 2 OSX drives & a confused time machine

Help - not only have I lost access to Microsoft since recent upgrade but time machine now seeing 2 hard drives, OSX and OSX-data, when I look at what’s on them they are a mirror image except that the OSX one has a new folder I created since the upgrade, haven’t done anything much else since as been trying to get support from Apple tech’s but the one I just spoke to said they have no idea why I have two separate OSX drives in “locations” and didn’t offer any advise just basically said “sorry can’t help you”, I am inclined to delete one of them but have no tech knowledge so scared I might completely knacker my iMac. I really want to get time machine back up and running as I don’t want to have to rely on memory to back up my stuff to a separate hardrive, I can see TM is working ok and have done a soft reset and first aid which shows it’s all ok but it keeps telling me it can’t back up because it can see two disks with the same name - any advise gratefully received.