Have you modified the system in any way, like installing Magisk?
What happens if you turn the phone off and connect it to your PC via USB while keeping Volume Down pressed? It should boot into fastbokt mode so you can change the active slot with fastboot --set-active=[a|b]. The current slot is written on top of the screeb.
You need to wait for the iodéOS logo to appear before you hold Vol. Down.
(Doesn’t vibrate in CalyxOS btw, still boots me into Safe Mode just fine if I keep holding it)
iodéOS 4.0 (LOS 20 based) has released yesterday as beta for first device batches
FP4
Pixel 4/5
OnePlus 9/9pro
Sony XZ2
So, after DivestOS (LOS) and calyxOS (AOSP) it is the third A13 ROM for FP4
…And it seems that it is running very smooth on FP4
At least there hasn’t been any negative feedback from the iodé community so far. But on the contrary
Edit 20230110
Yesterday, they released the second beta with January security patches
But remember what @mikeNG mentioned here:
https://forum.fairphone.com/t/fp4-and-lineageos/77347/602
As for re-locking the bootloader still applies to iodéOS as well
Official iodéOS 4 (Android 13) is out! 
XDA:
• Upgrade to iodéOS 4.0 based on Android 13 / LineageOS 20
• Blocker:
○ Improved blocking settings. You can now choose ‘Standard’ blocking (ads, trackers, malwares, etc) or ‘Reinforced’ blocking (same objective but more extensive), and then select additional categories.
○ The ‘Porn’ category has been extended to a wider ‘Sensitive content’ one, that also includes fake news, gambling, drugs, piracy, torrent…, with mainly child protection in mind.
○ The ‘Extreme’ category has been removed, as it is now part of the reinforced blocking.
○ Improved blocking lists. We merge several acknowledged and up-to-date sources, and have diversified our sources to produce more complete lists. The standard list has however been reduced a bit, to avoid as much as possible interference with apps expected behavior.
• Added a new network location provider: Local NLP Backend. It is an improved version of the DéjàVu NLP backend which was already available in iodéOS. Like DéjàVu, it builds a local database connecting localizations learned from other NLP backends and apps using GPS, and mobile antennas/Wifi; but also has an active mode (not preselected) that can trigger GPS requests. To configure it: Settings → System → microG → Location modules
• LineageOS synchronized with January security patch included
• All apps updated
• New devices support: Pixel 3, 6, 6a
I recently received my new FP4 and I’m still considering which custom ROM to install. iodé is currently my favored solution, but not 100% sure yet. What I’d like to do: just install iodéOS , try it out, install some apps that are important for me and check whether they run smoothly. If not, then I’d consider trying another custom ROM as well.
In that context, my question is: after flashing iodéOS, how easy is it to set back the FP4 to its original state? Or at least flash a different custom ROM? Or is there any" permanent" change introduced to the FP4 when installing iodé?
Of course, I’m aware that I need to the backup all the data and that I risk bricking the phone if something goes wrong during the process. My question is more about: is there some principle limitation to be expected, even if all the steps are executed correctly?
Not for the LineageOS bases ROMs, like iodéOS is, as long as you take care with locking the bootloader. Especially when returning back to stock.
As far as I know, only Ubuntu Touch may mess up with some sensors when reverting to stock, but this is reversable, too. You can read about it in the corresponding thread.
New and general features
4 Webview choices
as i know iode is the first security and privacy based custom ROM where I can choose between all of the the security based WV versions!!!
Hy all
I would like to try iode and running my FP4 currently with the latest version of calyxos. Can I just install the iode os or do I have to return to stock rom first? Any other things to consider? I just really dont want to brick my phone. Thank you all for advice!
You can install it directly that way:
or with my instaructions, which are already actual:
Two important things
be sure to remove calyx avb_custom_key before flashing iodèOS
fastboot erase avb_custom_key
before re-locking bootloader, be sure that:
check if bootloader unlock ability is possible =>fastboot flashing get_unlock_ability
→ (bootloader) get_unlock_ability: 1
==> if you get 1 then you can re-lock
==> if you get 0 do not lock bootloader
a good starting point for questions in case of problems is the iodé matrix room:
Thank you very much AlphaElwedritsch! I was able to install it today 
Everything went smooth - also locking the bootlader at the end with no issues at all.
are you @Scratch****** ?
Yes sir, the noob himself (lol)
Your participation is needed! What are you missing in iodéOS? What don’t you like? Just post your ideas there and/or poll. 
recycling week at iodé
This week 70 € discount for an iodé-FP3+ or iodé-FP4:
https://iode.tech/en/news/recycling-week-iode/
Finally, you can donate to iodé in a privacy-friendly way via bank transfer!
https://iode.tech/en/donations/#1679647947317-0973cbd9-e6ac
Great.
Kudos to iodè for completing the review very well.
Is iode planning new smartphones with military IP in terms of resistance?
