I painted a few brown wood grain plastic windows, white for my house 25 years ago.
They still look fine.
I cleaned them with panel wipe, sanded them, gave them another good clean with panel wipe, then plastic primer, 2k undercoat, let it dry, sand back to remove the grain effect then 2k top coat.
If the windows don't have a grain effect just apply the 2k direct to the unsanded primer. (if it's etecomended by the manufacturer)
If you haven't got the kit and PPE for 2k get someone else to do it or use 1k products which will work but won't last as long.