HTC U11 can't apply OTA (stuck on 2.42.400.2)

[sayapowa]

Hello everyone,
First of all thanks for being such a great community. I've been a silent reader for a while (since the HTC M7) and am amazed by the community

Now, I can't cope with being stuck on this issue anymore so I turn to you for ideas.

The situation:
I have a dual sim 128gb HTC U11 (I got it in Hong Kong but I assume it's the India version as per the build numbers I've been through and the CID is 060)
S-ON
Bootloader Unlocked
Stock 2.42.400.2 Firmware
TWRP Recovery
Magisk root

So a fairly simple setup.

The issue: We're in 2020 and I'm on Android 8.0.0. Checking for updates doesn't show anything at all although there are already updates
2.42.400.2 -> 2.42.400.6
2.42.400.6 -> 2.42.400.7
2.42.400.7 -> 3.35.400.1 (this is my goal, at least be on Android 9

So usually to update or apply an OTA which I would download from androidfilehost or another source here in a topic I would
1. Uninstall root from within the Magisk app
2. Flash stock recovery for my version back on
3. Put the OTA zip file on an microsd card and pop it in
4. update via stock recovery "apply update from sd"

Now that sadly didn't work. I tried adb sideloading the OTA zip file, but came to the same result below: (I had to hand type it off the screen so excuse any typos)

E:Failed to parse build number in post-build-incremental=1011554.6
E:Failed to parse build number in pre-build-incremental=1011554.2
O80CT.01.001.009
Source: htc/ocndugl_00400/htc_ocndugl:8.0/0/0/OPR6.170623.013/1011554.2:user/release-keys
Target: htc/ocndugl_00400/htc_ocndugl:8.0.0/OPR6.170623.013/1011554.6:user/release-keys
Verifying current system…
E:eek:riginal error message E1000: is set, why set another again?
E1000: system partition has unexpected contents
E:Error in /sideload/package.zip (Status 7)

Installation aborted

Any help is appreciated. I tried searching the forums for solutions but couldn't the same case.

Thanks and stay healthy everyone!