You can restore from backups but that would mean losing some progress, and they may not be useful if the oldest backup was taken a couple of days ago and you have been accidentally deleting notes for some time.
Alternatively, you can try restoring individual notes from the deleted.txt
file that Anki keeps in your profile folder. I don’t know how many notes Anki keeps there but it seems you can restore more notes than with the backup method.
This add-on seems to facilitate importing the notes again: Undelete deleted note - AnkiWeb
Also be sure to read the add-on docs: GitHub - Arthur-Milchior/anki-restore-deleted-note: Use deleted.txt content to put back note deleted