Help with "simple" remap on QWERTZ keyboard

[SirZayers]

I found the documentation very confusing, so I couldn't figure out how to remap a key to a "shifted" variant. Basically what I want to do is map
"ü" to "[" (so AltGr-8
"Ü" (S-ü) t0 "]"
"ö" to "(" (S-8)
"Ö" (S-ö) to ")" (S-9)
"ä" to "{" (AltGr-7)
"Ä" (S-ä) to "}" (AltGr-0)

but I just can't figure out how. Especially because evtest is showing "ü" as "KEY_LEFTBRACE", "ö" as "KEY_SEMICOLON" and "ä" as "KEY_APOSTROPHE".
I hope someone can help me. In my mind this shouldn't be a very complicated setup, but I still can't figure out how to do it.
I obviously want everything else to keep working as normal.
Thank you for any help.

[gerhard-h]

When you hold down shift all keys thereafter are normaly shifted (even if forked). To avoid that, I use (unicode ) to prevent S-RA-

(defalias
myü (fork RA-8 (unicode ]) (lsft rsft))
myä (fork RA-7 (unicode }) (lsft rsft))
myö (fork S-8 S-9 (lsft rsft))
)

If your linux has issues with unicode read

or you could try defoverrides (not tested)

(defoverrides
  (ü) (ralt 8)
  ;; repeat for all remaining 

  (lsft ü)  (ralt 9)
  ;; repeat for all remaining 
)

if you didn't set ü , ö , ä with deflocalkeys you have to call them by there US names [ ; ' as evtest told you.

[SirZayers]

When you say "all keys thereafter are shifted" do you mean that if I continue to hold down shift, it acts as it usually would, or that even when releasing shift after the combo, it continues to act like CapsLock? Because the first one is how I would like it to behave, the second one sounds like a bug.

So I have
(defsrc 7 8 9 [ ; ') (I want to remap ä,ö,ü to Shift-7,8,9 and Ä,Ö,Ü to AltGr-7,8,9 as I still need access to those keys

and then

(defalias
myü (fork RA-8 (unicode ]) (lsft rsft))
myä (fork RA-7 (unicode }) (lsft rsft))
myö (fork S-8 S-9 (lsft rsft))
)

and then

(deflayer base ? ? ? myü myä myö)

correct? Then what do I put for 7 8 9 in the base layer to enable ä,ö,ü again?
I guess I need to make a

(defalias
myü (fork RA-8 (unicode ]) (lsft rsft))
myä (fork RA-7 (unicode }) (lsft rsft))
myö (fork S-8 S-9 (lsft rsft))
my7 (switch (and (or lsft rsft) 7) ä break (RA-7) Ä break () 7 break)
my8 (switch (and (or lsft rsft) 8) ö break (RA-8) Ö break () 8 break)
my9 (switch (and (or lsft rsft) 9) ü break (RA-9) Ü break () 9 break)
)

(deflayer base my7 my8 my9 myü myö myä)

[gerhard-h]

without a deflocalkey section you must call keys by there english name ; instead of ö also keys have no upper case name like Ö it's S-;

(switch (7 lsft (or 7 rsft)) ; break (ralt 7) S-; break () 7 break)
would be
7 Ö nothing instead of
7 ö Ö
because the modifiers in the switch action are still active. The unicode trick works again:
(switch (7 lsft (or 7 rsft)) (unicode ö) break (ralt 7) (unicode Ö) break () 7 break)

[SirZayers]

So I don't need the "and"?
I thought the syntax was (or (7 lsft) (7 rsft))

[gerhard-h]

(switch (7 lsft (or 7 rsft)) (unicode ö) break (ralt 7) (unicode Ö) break () 7 break) worked when tested but it is in fact wrong as testing for 7 is not right. It should be written:
(switch (rsft lsft) (unicode ö) break (ralt) (unicode Ö) break () 7 break)

instead of (ralt) you may want

((or ralt (and lctl lalt)))