MakePass is an app that creates independent/proper Wallet *.pkpass files. You can completely customise the pass appearance according to Apple’s specs.

(Not sure whether the current licensing offerings are worth it, though. I’ve got grandfathered in from before it had AI support.)

https://pvieito.com

This looks like it would work well, but it’s a subscription. It makes no sense to charge me a yearly fee to make one pass file for my library card.

Look at Pass4Wallet - free from the start.

Commented in another reply, this is the answer. Works great and supports a dozen barcode types.

absolutely ridiculous. $10 for a single pass. I'd pay 99c for this app, and no more. Oh well, $0 it is.

What happens when they website goes away? The app I can save and use locally after the website is defunct.

Well for this particular functionality whatever you use (website, app, etc) must have a valid apple developer certificate, so either the website must be up, the app's backend server must be up, or an offline app's bundled certificate must still be valid. All of these things will eventually stop being true regardless of the form the app/website takes.

I don’t believe the apps do it local either. They need to send to server to properly sign the pkpass. A server is being used regardless.