On my side, I'm gonna wait until end of march, if nothing pop here (a statement at least), I think that will be a necessity by then.
Debian 10 LTS support ending on June 2024, that'll let me 3 months to get on something else (not Keyshit, don't like the way it's managed).
One of it's last statement (from Nuxwin) was that he found a few people to work on this project, but as we didn't hear back anything about this, I'm pretty unsure where we are on this ATM 
Moved to Spanish area... (+ not related to i-MSCP from what I can understand here...)
Debian 11, risky with this panel as with the last version published was to support Deb9, with some little to no-changes, you could go to Deb10 (which I'm using, still with LTS support, that's why I'm still using it), but Debian 11, there might be some changes to get a full support.
Hey,
If by "Custom DNS", you mean the use of the "Add a custom DNS record" (https:// PANEL/client/dns_add.php), well, for me that I've both OpenDKIM and PHPSwitcher (and also Let'sEncrypt), I never experienced such an issue (and I changed a lot of time the PHP Version in use since the initial setup 
So I'm afraid that I'll not be able to help you on your issue.
But, if you did modified some DNS listener file, this could be a bad implementation in those plugins, where the listener is not... listened (that's the only thing I can think of).
I only did the upgrade from Debian 9 to 10, never fully reinstalled it.
Now that some binary aren't available in the base repo of either "supported" distro, I would assume this to be quite difficult for a fresh install, but with some modification, this should be possible, need to be checked (you can try with a VM on your PC if you want).
This should help you if you want to test the upgrade : HowTo: I-MSCP 1.5.3 installation on Debian 10
As usual : Working backups are mandatory prior any majors system modifications.
Like someone else said on your specific topic, yes, 8.2.12 installed and working.
But yeah, Debian 10 need to be in use.
Edit : Please, do not post your query on all the topics you can find... one is way enough 
Thanks.
If you want to speak in german, here is the place to be : German Corner
Else, stay in english... it's not because the project looks dead that you have to overcome the rules in place.
You seems really mad... if you are not happy reitbrud , just leave with your rage.
I've all the plugins you cited here, all still work flawlessly on my setup... (including latest versions of PHP).
You switch over to another system ? nice for you, so why you keep posting there ?
