is it possible to change the colour of your own aircraft in the map and make it more visible (bright red or black instead of yellow).

In alternative, changing the track from black dotted line to continuous coloured ?

I have litlle Navmap on a second monitor and when I look at it to check my plane position, I find difficult to see it at a glance

 

 

You can change the flight plan, trail and user aircraft symbol size in LNM options:

You can also change the icon shape and color but you need a vector paint program like the free InkScape to do this:
https://www.littlenavmap.org/manuals/littlenavmap/release/2.6/en/CUSTOMIZE.html#icons

Alex