I've noticed some range issues with my setup: DJI Goggles Racing Edition.
Mavic Pro.
All devices with the latest firmware.
The area of use: Europe, Ireland (ROI)

I'm confused with all these information about the range I should be able to achieve with my setup in my country. Could somebody with more experience and better knowledge specify what range I can expect for reasonably undisrupted live video transmission (for both HD and 720p)? Let's assume I'll be flying far from the city (countryside) with low signal interferences and without any physical obstacles.

From my experience with the original Mavic pro and goggles RE's in 720p, you should
be able to reach your max distance. In HD or 1080p I've been able
to fly out 2.8 miles before it drop to 720p, but I have never had range issues.
Now with the Mavic 2 series that's a different story.