Accidentally deleted hard disks on 2017 MacBook Air

I had upgraded from macOS Catalina to Big Sur....and wanted to go back to Catalina. Went into disk utility and tried to recover with Time Machine. did not work so deleted disks. Did Internet OS reinstall which installed the original High Sierra OS that my MacBook shipped with. Went into disk utility again and saw the disk names had changed. Now showing one disk as : Macintosh HD-Data and the other as Update ?

High Sierra appears to be running ok, but now continually getting pop up message : Incompatable Disk this disk uses features that are not supported by this version of macOS. !!!! how can I revert back to the original disks that the Mac was shipped with ??

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