FP4, Pixel 4a and OnePlus 8 sure are good picks if you’re not strict on receiving firmware update, just having updated Lineage or e/OS. When it comes to hardware firmware support, Calyx has a table on this: Device Support
So if you’re very keen on firmware updates, buy even newer Pixel generations - if you care less, you can checkout anything that got added to the T / Android 20 build roster. If you scroll up that page and compare what vendor kernel your device SoC shipped with is a good indicator of longevity.
Devices that launched with Android 8-10 have a better future compared to your last Android 7 phone as you can go with GSIs when there is no device build anymore.