I am glad you adked. Since writing more hypothetically above, I have downloaded the 1.20-t ROM and can confirm that it contains e-recovery.
Late edit, payload-dumper-go reveals:
$ ./payload-dumper-go e-1.20-t-20240222382228-dev-enchilada.zip
Found partitions:
boot (67 MB), dtbo (8.4 MB), system (3.0 GB), vbmeta (8.2 kB), vendor (1.1 GB)
You just need to ensure that in Settings > Search > Update recovery, in Developer options is set to update recovery. Then your proposed sideload of the “fully loaded” ROM is expected to work.
(When you have an A /B slot phone you see the active slot displayed in e.recovery. It is useful to learn and understand how and when the slot changes. This is only my very general advice, there is no need to think it is a problem today.)
- Always have a backup before an intervention