alpha 13 update on the problem: I tried the same problems on the new "update" (version 12.5) and noticed these variations:
-the problem with the sun evolution still exists, albeit in a different fashion. The sun gets bigger and bigger like it should be, then it instantly becomes a little tiny sun (with the same texture of the normal sun), with the nomenclature "sun nova remnant" and "white dwarf" (even if the texture is not that of a white dwarf, but that of the sun, and there is no sign of " yellow dwarf ----> red giant ----> white dwarf" evolution passage whatsoever.
-the problem with realism and big stars has solved for some smaller stars, like Sirius B, but not for the bigger ones, like Betelgeuse and VY Canis Maioris. in these ones, when I switch realism on, they explode in novas, with the star still present though (a bit strange theoretically speaking LOL), and then instantly become neutron stars - black holes, with no gradual switch between the phases.
hope this helps. if the staff team needs videos of these new behaviours, please make me know.