Macintosh HD - Data After Reinstall

My 2017 iMac running Big Sur filled up and I was forced to erase and reinstall and migrate my data back from an external harddrive with a Time Machine backup. I followed these steps https://support.apple.com/en-us/HT208496 and everything seemed good, expect Time Machine did not seem to be making backups. I clicked on the Time Machine setting to run it manually and it timed down and prepared and then seemed to be done almost instantly. I restarted my iMac and tried again and this time Time Machine said it could not because there were two versions of Macintosh HD - Data. I looked in the finder and saw that where there used to be just my Macintosh HD listed, that now there was also Macintosh HD - Data listed below it.

Can someone advise me on what to do now and what I might have done wrong or what might have caused this?

Thanks,