Is your threat model really so severe that it includes someone driving to your house and connecting to your wifi network? Of all passwords, a wifi password is one you should _never_ reuse.

You could also inspect the source, it’s open source, or network requests.

opening in incognito tab with internet disconnected to make sure it works offline and that nothing gets sent after you close the incognito tab should be safe & secure but yeah you can also google the proper qr code format and make it yourself using qrencode in terminal or something like that...

but for semi-public WiFis like the ones in restaurants, hotels, ... it's a survivable risk

I don't, that's why having access to the source code is cool.