Can I limit my dock to only show up on the main display?
Your only options are both workarounds:


Uncheck "Displays have separate Spaces" under System Preferences > Mission Control
Pin dock to right or left instead of bottom (obviously not ideal if you're a bottom pinner)


More details here: https://www.makeuseof.com/tag/how-to-keep-the-mac-dock-on-one-screen-in-a-dual-monitor-setup/