Jeffrey Daniels, better known in the Commodore scene as Denial, has put together a quick reference handbook for the VIC-20.
Version 2 of this handbook covers the VIC-20, VC-20, and VIC-1001 systems, with the usual programming and reference material you’d expect from Commodore documentation.
https://jeffdaniels.itch.io/vic-20-quick-reference-handbook-version-2-vic20-vc-20-vic-20