How to disable the "virtual partner"

You are correct it cannot be disabled. There are a number of long threads on this topic.

For some reason, Garmin considers virtual partner that essential that it cannot be disabled; this despite the fact that so many users ask for this very simple implementation. Another contempt to Garmin's customers, their revenue source.

I saw something in this article recently where someone claimed to have disabled it using custom themes. I haven’t tested it and given the lengthy threads it probably won’t work, but needless ctccambridge.org.uk/.../garmin-tip-making-route-easier-to-see

That trick does not disable VP, it merely hides the the icon. CPU time is still wasted on calculating the position of the VP...those CPU cycles could be better used to improve navigation performance.

The “trick” works perfectly on x40 devices but unfortunately not fully on x30 as they don’t fully support all the MapTheme elements. Doesn’t work at all on 1050 as the MapTheme functions have been removed from them.

https://forums.garmin.com/sports-fitness/cycling/f/edge-1040-series/372871/hiding-the-virtual-partner 

The “traditional” trick with the VP is to set the course speed (which is used by the VP) very high so it races ahead or very low so it lags well behind. All still use processing cycles.