Welcome to the forum.
Getting straight seems can be dependant on the model. Here are some pointers that should help when the model geometry isn’t the problem. Note that “Scarf” seems will appear “scattered”.
- In the “Seam position” field use either “Aligned” or “Back”. I usually use Back and then orient the model where I want the seem. This was before there was the option to paint seams vertically.
- Paint the seam where you want it (Keyboard shortcut “P”). The newest version of Bambu Studio has a “Vertical” checkbox that makes straight seam painting SO much easier.