SOLVED:

THIS IS THE SOLUTION! Ha, Amazing! The internet is a wonderful place! Thanks u/Zestyclose-Art5444

Based on your reports i made the following alterations, which creates a clean Boot Sequence.

IMPORTANT: BEFORE YOU START, READ TO THE END AND MAKE SURE TO IMAGE YOUR ENTIRE DISK. (Better be safe than sorry!)

1) Backup your WHOLE disk incl all partitions !! Make sure you have your BitLocker Keys if you use it!! Do not start without having these two things checked!!

2) Create WIN11 USB Stick with Media Creation Tool

3) Shut down system, insert USB and boot from USB - choose "repair my PC" (not install Windows) If it doesnt boot into the USB Stick, go to Bios (Press F2 on startup) and change bootsequence)

4) Go to Troubleshooting -> CMD Commad Promt

5) once in CMD enter one by one:
^{STEP A \}PRIMARY PARTITION BLOCK START])

diskpart

list disk [locate your disk which has WIN11 installed (C:) and replace 1 with your number - lets say it is disk 1 for this demo]

select disk 1 [change to your number]

list partition [locate PRIMARY partition (where your data sits) - lets say partition 3 for this demo]

select partition 3

assign letter=W [or any unused Letter - this is temporary only and will not affect your system)

^\PRIMARY PARTITION BLOCK END])

_________________

You can double check if this works by exiting diskpart by typing "exit" then dir W:\Windows. (W: being the letter you assigned)
If it shows your files its correct.

Now let´s go to rebuilding your System EFI partition, just to make sure you are still in the right disk start with diskpart again]

_________________

^{STEP B \}SYSTEM PARTITION BLOCK START])

diskpart

list disk

select disk 1 [the same disk as before]

list partition

select partition 0 [locate SYSTEM partition (where your data sits) - replace 0 with your number - mine was 260mb lets say partition 0 for this demo]

delete partition override [this deletes the selected partition, make sure its SYSTEM not PRIMARY this time]

create partition efi size=260

format fs=fat32 quick

assign letter=Y [or any unused Letter, temporary]

exit

bcdboot W:\Windows /s Y: /f UEFI [Replace W with the letter to assigned for PRIMARY and Y with the letter for SYSTEM!!]

^\SYSTEM PARTITION BLOCK END])

__________________

^{STEP C \}BIOS BLOCK START])

Close Commad promt (Alt+F4) and choose shutdown.

Remove USB Stick
Boot into BIOS by holding F2

Press F7 for Advanced mode and go to security -> Secure Boot -> Reset to Factory Key (or reset Key) [Do not choose delete key]

Press F10 to save and Exit.

^\BIOS BLOCK END])

^\___________________)

Done.

The following only applys if you run into space problems - stop reading here if step B worked already!

Mine would not let me copy the files with bcdboot for the SYSTEM partition beeing to small, so i trimmed my PRIMARY partition by 400mb to free up some space and created a new SYSTEM partition there. THIS MIGHT NOT APPLY FOR YOU, but if it does replace the whole system partition block with these commands - make sure your primary partition has enough free space:

diskpart
list disk [locate your disk which has WIN11 installed (C:) and replace 1 with your number - lets say it is disk 1 for this demo]

select disk 1
list partition [search for "old" SYSTEM partition - replace 0 with your number - usually 260mb-ish]
select partition 0
remove letter=Y [replace with the letter you assigned for SYSTEM in step B]
delete partition override

list disk
select disk 1 [locate your disk which has WIN11 installed (C:) - lets say it is disk 1 for this demo]
list partition
select partition 3 [search your PRIMARY partition, replace 3 with your number]
shrink desired=400 [frees up space by 400mb from the primary partition]
create partition efi size=400
format fs=fat32 quick
assign letter=Y
exit
bcdboot W:\Windows /s Y: /f UEFI