Could you not download the APK for that apps and installed directly?

Don't get me wrong, I had not realised google was locking the play store and totally agree that it is an issue, but wondering if that could have helped you at the time.

Also, I run lineageOS to be able to update old phones with recent Android version, and tend to get better battery life and faster boot!

I have a "workaround" for you: On another phone, download the apps, and you can transfer the APK to your phone to install the app without the play store. You can also download alternative to google play store.

Unfortunately there's no Google Pay equivalent, right?

To pay for Google's services? Yes, you would be right.

I meant for contactless payment - I'd be interested to see how an open version of that could ever develop.

Why not just use the contactless card your bank gives you? Or, if you don't want to pay directly out of your checking account, get a credit/pre-paid card? They are all contactless these days, and even the small tea shop that processes card payments through an Android tablet and a small Bluetooth reader is able to accept the contactless cards.

Two reasons:

1. My bank doesn't give me a contactless card

2. It's much more convenient anyway, I don't have to reach into my wallet.