The latest pixel devices (since 6 I think?) already provide accees to a /dev/kvm device, so maybe you could even run a normal Ubuntu server VM on your phone for hosting these services.

I guess he means that raspberry pi doesn't run a mainline kernel

Although it's true that you are increasing the attack surface when compared to locally stored OTP keys, in the context of OTPs, it doesn't matter. It still is doing it's job as the second factor of authentication. The password is something you know, and the OTP is something you have (your phone/SIM card).

I would argue it is much worse what 1Password and Bitwarden (and maybe others?) allows the users to do. Which is to have the both the password and the OTP generator inside the same vault. For all intents and purposes this becomes a single factor as both are now something you know (the password to your vault).

Made my own for myself and some friends. We couldn't be bothered creating account on the larger instances and have power tripping admins de-federating instances over trivial issues.

I think those kind of vulnerabilities are pretty rare, though.

Not really... If you go read the security bulletin from google, you will see every month that there are a couple of issues fixed on closed source components https://source.android.com/docs/security/bulletin/2023-07-01

Also vulnerabilities related to kernel code, I highly doubt most ROM "developers" are actually backporting security fixes for that specific device's kernel branch/source.

You can update your phone with custom ROMs, but it won't update the closed source components of it(device drivers, bootloader, etc...). If a vulnerability is found in one of those components, it's unlikely that it will get parched

I think bitwarden fills all of your requirements.

In Europe I would say debit cards are way more common than credit cards. It's very rare to see someone paying with a credit card.

I ran GrapheneOS on a pixel 5 but ultimately went back to stock.

GrapheneOS was considerably slower on my phone. Apps took a bit longer to loader, but the worst was installing APKs, it takes so much longer compared to stock. Some apps (e.g. revolut) took more than 5 minutes to install, it was crazy.

I’d know if someone had any access to my phone

This is really a bold claim. How or why makes you so sure of that?

If the attacker/app manages to get some application running in the background as root, how would you know that they had access to your phone?

Am I naïve for thinking that manufacturers stopping support for devices, then claiming it affects your safety, is just to sell more phones?

Yes you are.

Vulnerabilities are constantly being found in the software stack used by Android, if you are running vulnerable software you're increasing the likelihood of some malicious app (or website, file, etc...) taking advantage of the vulnerability. The consequences of vulnerability vary from being able to fingerprint your device when it's not supposed, to escalateling privileges to root or even kernel mode. Although the later are significantly rarer.

and had zero security issues in a dozen years

That you know of... If the vulnerability is successfully exploited, the likelihood of you noticing are close to zero.

You could always flash a custom ROM to install the latest security patches, but you would still be missing the security updates for all the closed source components (such as the bootloader, device drivers, etc...). Not to mention all the security implications (good or bad) that comes with installing custom ROMs.

What kind of "control" do you mean? Your posts/comments get replicated across all the other instances. You can't really "guarantee" a delete, since the other instances might just ignore your request for delete.