Regarding the two volumes that show up in Disk Utility, macOS Catalina introduced a new system volume which you can read about [link|https://support.apple.com/en-us/HT210650|here]. It sounds like the OS was damaged during the attempted software update. Since First Aid is not able to resolve the issue, I would recommend attempting to reinstall macOS. [link|https://support.apple.com/en-us/HT204904|Here] are some instructions to help you reinstall macOS on your computer. If you just need to backup your data you may need to boot into a bootable external drive running a similar version of macOS - from there you might be able to access the data on the internal drive. I hope this helps!