Update
My Mac has stalled while updating I think the update may have been fo Big Sur which I have not got I can’t turn off what do I do now . I have the Apple logo and the download bar on my screen. Help .
MacBook Air 13″, macOS 10.15
Restart in Safe Mode - immediately at stirrup hold Shift key. Remove any and all external drives before restart.
If required. Shut down by holding the Power Button then restart as above.