Russian here and here how it will probably go.

I would emigrate and work against my country of origin in a heartbeat if they started a war of aggression (hello Russians) - unchanged from before

You will emigrate and either work with a charity organization that helps refugees from the other side (often refusing help to your nationality because they are Orks) or you will start helping the military on the other side, which would seem righteous to you until this military starts to neglect collateral damage.

I used to work in a charity that helps refugees here in Georgia. I still donate but I was unable to comprehend the very people that we were helping up calling me an occupant.

When Ukraine started shelling and droning Belgorod, many of my Russian friends stopped military donations.

I would support with my medical and other skills those defending a non-aggressive country I live in

That's actually what will happen, yes. Rally 'round the flag effect is real and those of my acquaintances who happened to be communists in Ukraine have been supporting the military and Zelensky given the communism is banned in Ukraine.

I might fight, given no other choice. But I would try everything else first, and I would probably not be good at it (fighting) at all.

And you will either end up with PTSD, screaming in the middle of the night, or dead. Don't do it unless you really believe that you are fighting for things that are more important than you yourself.