Adding recessed lights in basement
The light fixture doesn’t say it has to be on a 20A circuit. It says you can add a maximum of 8-#12 wires (coming/going) in its junction box. In other words, a max of 8 wires and a max of #12 gauge.
You can have less wires as needed, and the only other allowable gauge wire would be #14, which is smaller and would have to have a breaker/fuse no larger than 15A.
Also, the wording on the fixture does not have anything to do with the number of fixtures on the circuit. That is found by doing a circuit load calculation (in the US…not sure about Canada).
Just because you can, doesn't always mean you should