I don’t understand how their solution differs from what currently happens at any other big site like reddit.

Must create account and then there’s scraping resistance by captcha and rate limiting.

Gog games are also digitally signed. So you can check the signer and know it hasn’t been tampered with.

That’s true. But they do give you easy, portable, site specific passwords. No apps or database syncing required.

If you just want to log in to Lemmy on a work computer at lunch it seems a good option to me.

There’s a few. LessPass is one that has been going a few years.