Hereforhelp1991 video calls, watch films, navigation
If you can provide a very specific example maybe somebody can try doing that exact thing with the same phone you have, and can report whether their experience is the same as yours - perhaps their device will also be hot, or perhaps it will not. But generalizations are not repeatable in a comparable way.
For example, if you report that playing a particular 10 minutes of some specific video in Vanadium makes your phone hot, somebody else could try playing those minutes of that same video - perhaps somebody running GrapheneOS and somebody else running the stock Google OS.
The point made above, that charging inherently produces heat, and charging at the same time as your phone is working hard inherently produces more heat, is certainly true. That sort of general observation may be enough for the circumstances. If not, moving from generalities to one or more specific detailed examples may be a good idea.