/e/ is a Custom ROM. Nobody can guarantee the functionality you mentioned anyway.
The switch to Magisk comes from LineageOS, they dropped their own addonsu.zip.
Not in the same way, if at all.
The Fairphone 3 is an A/B device doing seamless updates, which work differently than before.
Define bricked.
Even if Fastboot Mode doesn’t work anymore, not all hope is lost with the Fairphone 3.
Plain wrong, where did you get this from?
Of course you can install TWRP, if you choose so. Installation procedure is given on the official TWRP page … https://twrp.me/fairphone/fairphone3.html.
Whether it is advisable to install it instead of just booting it when needed depends, as installing it changes the boot partition. There is no recovery partition to just flash it to.
I had no luck with restoring all partitions with TWRP in one go, but installing the OS from scratch, setting up encryption like it was before and then restoring just the data partition was looking good when I tried.