The event chain has to be followed like this, with the following conditions:

Start as Brandenburg with your Wittelsbach ruler

1. Switch your vote to Bohemia and hope he gets elected in the first 10-20 Years
2. Bohemia's Luxembourg Dynasty MUST get elected and Wittelsbach HRE Emperor MUST die before you get to -20 "Wittelsbacher investment"
3. You MUST get to -20 Wittelsbacher investment (bottom option that starts at -15) so the Wittelsbachs will leave Brandenburg
Avoid the Askanier pretender event, don't pick the historical option, reload or pick the "banish him" option
4. You MUST have Bohemia give you one of his sons as Ruler (Jindrich of Luxembourg Dynasty, usually)
5. Bohemias ruler ,Jehan The Blind, MUST die with his son, Karel taking over
6. YOUR Luxembourg Dynasty Ruler must die now, resulting in Bohemia getting an event to put Friedrich (his adviser) on YOUR Throne

Tag Switch to the countries you get the events with to improve your outcome (like to Bohemia or Bavaria) and pick the responds option you want, yourself. You can do this by enabling tag switching in the game rules and then hold CTRL+Left Click to switch country
Additionally, type
kill tag (kill BOH)
to kill Bohemias ruler via console to make it faster or trouble shoot the event chain yourself




If these things happen in your game, then you should be able to make it happen.
RNG is involved so i suggest either lots of saving and restarting will be happening.

This is the Event ID for Bohemia to give you Friedrich von Hohenzollern:
flavor_bra_dynasty.1201.a
To open in-game console type
-debug_mode
Into your Launch Options in Steam



Leave me comments so i can update and make this more accurate