I'm not sure that is necessary to go that far, unless one wants to. Both Volla and Jolla phones and Fairphone 5 version with /e/os are all degoogled out of the factory. Sailfish and Ubuntu touch are great Smartphone OS options. If you haven't tried it on someone else's phone, you should, they're both really great.
But I completely support people using dumbphones. Getting away from the hassle and hustle of an app centered world is quite refreshing.
I've degoogled my Samsung Android quite a while ago. And, no, I don't have Google Play Services in the background either. Completely degoogled. If you don't know how to jailbreak it to remove the apps entirely, you can just deactivate the apps and uninstall the updates from them. It will free a lot of space and memory and your battery will last longer. My phone is over 5 years old and the battery lasts over 4 days. Although I only have two non-system apps installed, voyager for Lemmy and Pixelfed. And when I travel and need directions I install Herewego or Mapy. I take turns between them. When I don't need them, I uninstall them. And that's it. No Meta shit (no, not WhatsApp either), no youtube, nothing. I do my banking in person. Malware is getting too good too fast with A.I. as a sidekick for hackers. This is a huge cybersecurity concern all over. One can risk it out of convenience, I won't. If the bank gets fucked on their end, the money is ensured, if I get fucked on my end, it isn't. It's that simple.
Anyway, there are decent European alternatives for both Smartphones and Dumbphones. And yes, we should support them. Apple, Google, Meta and Microsoft are some of the worst companies out there.