Just for information, this link Feedback for v3.0 - #203 by nicofonk describes a method suitable to adb sideload an updated image (hopefully without loss of data, but backup essentials before any intervention).
- on “a phone with a problem”
- a phone like an fp4 where only an Install ROM is published and documented, that is there is no “manual update” documentation.
Edit. adb sideload is the old school way to do an “everyday” manual update where userdata is not impacted.
Edit 2. The above method includes the way to strip IMG- within the Install-filename url. (Easy when it is explained well there). You can alternatively collect an OTA_PACKAGE from ota.ecloud.global/api/v1/FP4/official to find your downloadable image please search for "url".
Edit 3. I did suggest a non-sideload method but using the Updater (if it is competent for you) here Feedback for v3.0 - #521 by aibd