According to community feedback on similar topographical downloads:
: Use a tool like 7-Zip or The Unarchiver to decompress the .7z file. TOPO1a.7z
“Map manager is finicky for me. Garmin express says up to date but on the watch I have updated pending that never download.” Reddit · r/GarminFenix · 1 year ago Installation Steps TOPO1a.7z