There's no getting around having a SIM since you'll likely need to use navigation programs like Waze when you're in the car and WiFi is unavailable.

The magic combination for me personally is:

GrapheneOS

Buy an esim using Bitcoin from silent.link. It's a data-only plan. No voice or SMS. No phone number. They'll assign you an IP address from some obscure location like Warsaw, Poland. So far so good, but the IP address is attached to your esim which is attached to your location.

Now apply ProtonVPN, also paid for in Bitcoin. You've now decoupled your IP address from the esim and your physical location. The VPN IP address is what WhatsApp, Telegram, Signal, etc. will see. Make sure to turn on the GrapheneOS option to block all outbound connections unless the VPN is connected.

So far so good, but you still don't have a phone number or SMS. So for that next step, get a phone number from jmp.chat. Pay for it in Bitcoin. There are no esims associated with that phone number. It runs over XMPP. The only thing jmp.chat will know about you is your anonymous VPN IP address. You've now decoupled your phone number from both your (real) IP address and your physical location.

Your use case seems to be like mine; Very little voice phone or SMS. But when you need it, you need it. So now you have a phone number. The latency with all these layers will make voice calls over jmp.chat rather sketchy on the road, but it'll be fine when you're connected to WiFi.

This seems to be the magic combo for me. The only shortcoming is that financial institutions like Bank of America, Charles Schwab, etc. won't send TFA codes over SMS to a VoIP phone number, and jmp.chat is definitely a VoIP number. I try to avoid companies that insist on using SMS TFA codes, but if that's a critical use case for you personally, you'd need a cheap dedicated flip phone and plan for that.

Hope this helps.