I’m interested in getting an Insta360 X5 camera to contribute, but the examples I’ve seen don’t have the necessary resolution to see, for example, street signs and business names that aren’t very close to the camera.
Are there any examples in Mapillary of street imagery taken with the Insta360 X5 (or the GoPro Max 2) that have been optimally processed and uploaded, to get a feel for how good the quality is?
Yes, there are examples of both if you do a quick search in this forum. However note that the examples on Mapillary are compressed (not original quality for speed and filesize reasons)
Go for the GoPro MAX2 because it has a built‑in GPS receiver. The Insta360 X5 does not. Automation is 
king in a mapping workflow. X5’s lack of this feature alone makes it a no contest decision for mapping. Do not get swayed by mambo jumbo marketing promises that you can connect the camera to your phone and record GPX tracks or the like on your phone using its GPS receiver. None of this works as you would expect. You will thank us later.
Great, thanks!