They are most likely referring to `tensorman` https://support.system76.com/articles/tensorman/ which is regrettably premised on the notion that you have any intention of using Tensorflow in the first place.

Unfortunately, the `tensorman` article shows up first (after several complaint/support threads) in a google search result for the subject https://www.google.com/search?hl=en&q=nvidia%20docker%20pop%...

In all actuality, the correct article to reference is https://support.system76.com/articles/cuda/ but alas, this is presently broken on PopOS 21.04 unless you pin nvidia's repo's as you've suggested.

At the very least, an unpleasant experience. Probably some blame to be shared by system76 and nvidia.