One thing to consider is that App URLs end with glide.page whereas Classic App URLs end with glideapp.io. The url will be different, and there is no way for new Apps to use the old glideapp.io domain.
You may be getting ‘Not Found’ because the url is no longer the same.
This is only an issue if you use Glide’s urls. If you have a custom domain then you will still be able to move that custom domain from a Classic App to a new App with minimal effect on the users. At most, they may need to sign in again.
In my case I didn’t because I sell credits on subscription. But in the case of controlling visibility - row owners for data and filters for component or sheet visibility, I’d imagine.
Do you all have any ideas on how to use stripe payment links to show that a specific user has purchased something? Like being able to set a flag in the users row. I’m wondering how much pain I’m in for to try to lookup email addresses and then set flags…