Trying to actually restore is the best way to ensure the backup works. But it’s annoying so I never do it.

I usually trust restic to do it’s job. Validating that the files are there and are readable can be done with restic mount, and you’ve mentioned restic check.

The best way to ensure your data is safe is to do a second backup with another tool. And keep your keys safe and accessible. A remote backup has no use of the keys burned down.