I built a pretty good profile to use the Pixel 3a with a Daydream V1 viewer (as a Cardboard viewer):

{{::daydreamv1-pixel3a.png?nolink|}}

If, like me, you are coming from a Daydream experience, here are examples of what you can still do with Cardboard:
- View Youtube videos by using the normal Youtube app and in the options switching to VR
- View panoramas from Google Photos. Search for panorama, open a photo, there is a cardboard icon on the bottom.

These require to often remove the phone from the viewer.

For VR video, I found VRTV to work quite well. You can open videos by using the touch screen or from an interface while in the viewer. You're able to select things and use the interface by looking at icons for a while.

Not as good as Daydream of course, but coming from a Pixel 1 that was overheating, here at least the phone remains cool enough so it's actually worse and better depending on the aspects.