ttrpg player pro tip- just tell your GM when you have a plot in mind for your character. Ask for events to happen. Walk up and say "I want my evil brother to show up and be a huge fight and I try to save him from himself." Your GM will ADORE having a whole encounter outlined for her, you'll get to have an awesome scene play out, you'll be invested, your GM will be invested, it'll be memorable. Hopefully, just don't be foreceful.
The idea that you and your GM will be able to like, psychically intuit each other's ideas for character arcs is bullshit. This is a collaborative relationship; communicate!!
Also get comfortable undoing shit if you're the DM. If you made an off-hand comment that didn't fit the world you want to weave or if you realized an event would have long-term consequences you don't want. You can just pause and tell everyone "wait I changed my mind, forget I said that! it didn't happen." and go back to the previous scene.
Ultimately ttrpgs should be a fun play time; ask yourself if you're following invisible rules, and if those rules help or hinder your game experience.