my *really* old phone
I have a Oneplus 5, and only T-Mobile will allow it on their network (AT&T needs the final Oneplus 6 model, even though this supports VoLTE).
I was already running Lineage on it, but I wiped back to stock because I needed a phone for Cisco Duo (remote access . So I ran on Android 10 for 3 years or so until Duo ended support for this OS release. I mailed the corporate security people about putting Lineage back on with MindTheGapps Google support, and they said that they did not explicitly forbid it, so I brought it back to Lineage's release, currently on Android 14 after the upgrade this month.
Suprisingly, even Wells Fargo's app runs.
Many Android people say an unlocked bootloader is an insecure phone because it is vulnerable to the "evil maid" attack. However, an OEM-abandoned phone running the latest LineageOS release will have updated network security patches that might be more valuable in trade. Note that any firmware vulnerabilities with your WiFi, Bluetooth, LTE/5g modem might present an attack surface that cannot be patched, but a 3rd-party ROM allows you to keep at least *some* of the device up to date.
The Pixel is an even better device, so by all means try a custom ROM.