I hope you didn’t actually flash TWRP, otherwise you’ll have to restore the stock recovery (and boot anyway of course) before you’ll be able to install the next OTA.
Keep that in mind if your next update fails.
The latest factory images are already available BTW, no need to mess with TWRP or otherwise dding partitions from a running system.
I mean it’s a great learning experience, but the boot.img is right there for the taking 
I did flash TWRP, I tried a few times to ‘flash boot twrp.img’ but it would just freeze and I would have to hold down VolDown + Power to reboot. Is there a trick to booting TWRP?
Are suggesting I flash the whole stock image on with the following instructions;
No, you don’t need to flash it.
Just download the factory images, extract the archive and the boot.img you wanted is right there 
Can’t help you with TWRP, I don’t use it, sorry.
Since you flashed it, you might want to hold on to the factory images you downloaded, because you will have to flash stock recovery before you can update to the next OTA.
So I could download the latest FP4 stock Android 12 image, extract it and flash just the recovery to get rid of the TWRP, or should I revert back to the full stock Android 12 image and then try to root it again without flashing TWRP?
You only need to flash recovery.
Regardless of what you do now, you’ll also have to follow the OTA update instructions at the bottom of this post, once an update arrives.
This is turning very off topic, for further Magisk related questions please follow up in the dedicated root topic.
Received the update today on KPN in The Netherlands. Update went smooth and no issues so far. 
Is there still anyone unfortunate with Android 11 on the phone? I’m talking to support about a behavior change, but I base it just on my gut feeling, so it would be nice to have some hard evidence
What bothers me is that when the phone is in my pocket (i.e. proximity sensor says CLOSE and ambient light sensor says low values) and a notification is received, then the display shows the notification on black background (that’s the same), but on A12 it also activates the touchscreen. My gut feeling is that on A11, this black-background notification screen did not react to touches and I actually had to press the power button to interact with the phone (with the exception of incoming calls and alarm, of course). The easiest way to test this is lock the phone, send an SMS to the locked phone from another phone, and try to touch the screen. Now, take a piece of something non-conductive (e.g. cardboard) and lay it over the top 2cm of the phone so that the proximity and lighting sensors are covered. Repeat the thing with SMS and trying to touch-interact.
I’d be really glad if anyone still on A11 could help me with recording a video (or just telling me my gut feeling is wrong and the touchscreen activated also on A11).
The problem I have with this behavior is that once or twice a day I pull the phone from my pocket with lots of numbers typed to the emergency calling screen. I can’t find any other explanation than this unwanted activation of the touchscreen.
The support told me to disable waking the screen for notifications, which could help, but I want to retain this visual part. I just want to get rid of the interaction part of it.
Thanks!
Are you sure the phone is really locking? And are you sure you dont touch the fingerprint sensor and just unlock the phone? I havent noticed this behaviour I have the phone in my pocket a lot…
https://forum.fairphone.com/t/screen-time-out-does-not-always-work-on-fp4-in-android-12/94460/5
Edit: I tested it with A12 as you described and surprise surprise, you are correct…
And overall just another sensor issue, to add to the list…
Edit 2: does not happen always or it only happens when I dont only touch but swipe up slightly🤔
Just lay the phone on a table and touch it from above =) 100% no fingerprint sensor touch 
So you say tapping the notification does nothing, but swiping up does?
It seems when I tap on the Notification itself, the screen unlock pad shows up to enter the unlock Pin, however it seems nothing happens when I tap the screen somewhere else (unless I accidently swipe up slightly instead of just tapping)…
I put my physical SIM into my FP3 with Iode A12 and it seems to behave the same: tapping on the notification on the otherwise locked screen will open the unlock pin pad…only difference: on the FP3 the notification does not show up until I activate using the power button…
Is this still intended on the FP4 as there is no notification LED? Or do I miss a setting on the FP3?
Yes - because “aptX HD” is not “aptX”. Only “aptX HD” was fixed, but not “aptX” or “aptX adaptive”.
Yes, this is the intended behaviour. You can change this in the settings:
Notifications → Notifications on lock screen - this will control if Notifications are displayed at all on the lockscreen
Lockscreen → Wake screen for notifications - this will control if the lock screen will be turned on for a moment when new notifications are displayed.
I know where to set this on the FP4…
I see. I just checked, it’s indeed aptX, not aptX HD that is available with my headphones.
I’ve noticed 2 more bugs though (unrelated to the aptX thing):
For Point 2 sounds like a nice reproducible bug. Worth contacting Support.
For Point 1 there’s already lots of discussion.
I had the behavior with a Sandisk MicroSD card in A11. The only thing that helped was getting a different micro sd card for me (from Samsung)
Does the samsung card work well on the fairphone 4 now? Because I was thinking about upgrading to a 1TB card anyway, and this would be a good excuse (I’m using a 400GB SanDisk card right now).
I’ve got a 512 one, everything is ok.
I bought a SAMSUNG EVO Plus Micro-SDXC 512 GB in December and since then it is working fine as mobile storage