Isn't there qr codes that can automatically update their values? That could work.

Otherwise just buying those picture viewers and setting a qr image would be easiest.

A picture of a QR code will always be the same QR code. There are QR code generators that purport to let you update the value... but they're basically just hosting a link shortener service, giving you a QR code encoding that link, and letting you change where the link redirects to. That wouldn't work with a QR code for wifi, since the QR code does not point to a link, it directly encodes the SSID and password for a wifi network.

Can the http link not be directed to other protocols like FTP, or WIFI:T:WPA;S:{ssid};P:{password};; in this case? I guess this might have some security implication. And, some clients can block such redirection.

I tried with HTML href on my mac. It didn't work. Maybe it'd work on phones.

The dynamic vs static is also one of the criticisms to NFTs. They're just links to dynamic content in a distributed database. The content itself could change any time, or go down. But it looks like it works (there's a word for this: scam).

How would you use a dynamic link like HTTPS URL shortener if you're trying to achieve internet access? You could overcomplicate it with another AP which only works with QR code.

A colleague once painted a QR code, kinda cool its possible and it worked, but its no magic. Its just static content. If you want it to be dynamic, e-ink is perfect for this purpose. It doesn't require electricity, only if you change the content. So if it is say a Raspberry Pi Zero, it could be powered off, and only get powered on when required (even the e-ink screen itself could be detached).

I know they use captive portals a lot for this purpose but I don't see how say WPA2/3 Enterprise could not work for this.

How is your guest going to visit the link when they're not yet connected to the wifi?