Its a similar problem with Proton for me. Proton doesn’t even let you sync to 3rd party cal app on the free tier.
If you’re going to paywall basic functionality, that just prevents me from trying it for a while and eventually become so tied to it, it’s difficult to break free. Google had the right plan from the get-go.
Try out Privacy.com for online shopping. Also use gift cards where possible.
For physical, cash is king, followed by gift cards. Visa prepaid cards are a solid choice, but not really practical.
Failing that, I’m not sure you can find a private card, not that I’ve looked.