I had the same issue with my wife until she tried to start her own thing. We fought like cats and dogs because of how much of a wet blanket she was even with my successes. The fights have completely gone away after she tried starting up her own thing and saw how me being positive help so much and when somebody comes in like a stick in the mud that you anticipated being helpful and giving you at least positive advice wasn't. I don't hang it over her head, but she and I both know that her negativity took the wind out of my sails. And it's a shitty way for a partner to be.
I don't know if it's possible but tell her to start up her own thing separately from you. You won't even need to criticize her all you need to do is be supportive like you want somebody to be with you. You don't know until you know, you know
Starting something you believe in is hard. Just don't lose the passion with burnout. Yes it's mentally and physically exhausting yes it's financially draining yes it takes up all of your time and kills your social life... but once it gets going by itself it gets a lot better.