It seems you are coming from a Fairphone 2 to a Fairphone 3+.
Some things work differently now. Like many Android phones nowadays, the Fairphone 3/3+ is an A/B device.
When you installed TWRP, you will have noticed the different, more complicated procedure compared to just flashing it to the recovery partition on non-A/B phones.
Installing TWRP now alters the boot partition. This breaks Fairphone OS OTA updates (because the Updater there checks for altered partitions and quits the process in case there are any), and /e/ just restores an unaltered boot partition with its own recovery with every update.
The recovery is not needed for updates anymore. If you have a look into the update ZIP files, you’ll see how it’s just the partition images in there, no update script, no anything else.
When updating via the Updater, the update gets installed to the A/B slot you don’t currently have in use, this happens in the background while you are still using the phone, then the active slot gets simply switched with a reboot and you’re back with the new OS version without the installing delay of old.
If something went wrong, normally you could switch back to the OS state prior to the update, the data would be the same (only the OS is A/B).
I guess you need to check whether TWRP is able to install the images ony by one to the correct partition in the correct slot, emulating what the Updater does automatically.
TWRP should still be able to install images (like back on the Fairphone 2 you could install the TWRP image with TWRP to the boot partition or to the recovery partition), and TWRP can set the OS slot, but I don’t know whether TWRP now would give you the correct targets for the partition images.