https://learn.onshape.com/learn/learning-path/introduction-to-cad :
https://www.frcdesign.org/learning-course/ : FRC focused but the first unit is universal.
Parts library from Purple Gears
goBILDA:
REV Robotics:
REV Robotics parts on 3D Content Central - Seems mostly updated. Need a login to download.
Look up parts on REV Robotics website to download without login
TETRIX MAX:
TETRIX MAX parts on 3D Content Central - Seems mostly updated. Need a login to download.
Look up parts on Pitsco's website to download without login