I've had no luck getting Alipay to work with any foreign (non-Chinese) card, tried multiple Visa and Amex cards.

Alipay is confusing, because non-Mainland cards may work for a few things and a few things only. I've never seen a chart showing the limitations, so it's trial and error.

I think for non-Chinese cards, you pretty much have to use a debit card for Alipay as a foreigner.

No, I've used a non-Mainland credit card on Alipay for Taobao/TMall purchases and mobile top-ups. But no QR code for instant payments without a Chinese bank card that works for real-name registration (many don't for foreigners).

Also, payment options on Alipay seem to vary depending on whether you're using the mobile app or desktop version.

For real name authentication, you can submit your foreign passport and valid Chinese visa. My Alipay and WeChat wallet both authenticated perfectly.

My accounts are authenticated, and I have no problem doing QR code instant payments or sending money to friends, as long as the funding source is either a Chinese bankcard or "wallet". But, my foreign cards only work for merchants like Didi, Ctrip, and Unicom.

You can only authenticate if your Mainland bank supports real-name authentication using passports on Alipay or Wechat. Only some do. I posted the list of banks that work on another thread here.