I've downloaded the topographic map for Europe but I still can't see any detail? All I see are major roads.

I assume you downloaded the Garmin ️TopoActive maps? There is a eastern, western and central europe map. Which one is active and where are you located?

I'm in the UK and have downloaded the Western European map.

Then I would try to reinstall the map via Garmin Express. Seems like the downloaded map is somehow defective 

I've deleted and re-downloaded twice.  Doesn't seem to make any difference.

Now I remember that some time ago, somebody reported that a part of the UK map was missing for him. I cannot find this thread now and i cannot remember if there was a solution...  

Maybe just to check if only a part of the map is missing, could you scroll down to France or Spain and check if there are more details?

If you want a fast solution, I would recommend downloading a 3rd party map and place the img file into the GARMIN folder via PC. I am a fan of the map project of fellow forum member Bumskopf

You can get the Great Britain map here: https://downloads.andrehotzler.de/freizeitkarte-osm-customized/04_2024/Freizeitkarte_GBR_en/

(I would start with the default img download, then there is also one without buildings and without buildings and less POIs, if the default one is too slow)

Additionaly, I would get in contact with Garmin support to fix the issue with the TopoActive map.

DId you marked in activity whicm map will be active for it?
I assume you have proper map on your watch just not active.

FOr rest, read manual how to enable map on the watch.