I solved this issue with Wallet Creator: https://apps.apple.com/app/id1486573384

Didn't know it was this simple to just provide a download for prepared file. Is it open source?

I tried using this. The camera didn’t work in several ways, it didn’t understand barcodes, and crashed a half dozen times before I just deleted it.

I don’t see it that way. I would rather have a browser based, one-off tool that can generate a .pkpass served up for local “installation”, not installing an app that is necessary to separately manage the passes separately and very well could be tracking its users.

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.