Just started to configure and deploy a new router - Linksys Velop WRT Pro7 with Luci interface. I don't see where or how to setup MAC address filtering. This router appears to be using OpenWrt 19.07-9 and don't see this router in the list of firmware updates.
As you have probably already guessed, the OpenWrt project does not support that device. What you are seeing is a vendor firmware that is derived from an ancient release (19.07.9 was over 4 years ago, and has been superceded by 5 major releases in that time).
Because what you're using is from Linksys, you'll need to reach out to them for help.