A steam deck is basically an arch linux laptop. I bet there are ways you could connect it to a bigger monitor and keyboard to simulate a proper pc though part of why it performs well might be the lower res for the smaller internal display.
There are some great free options to learn game design. Godot, blender. I am most certain its doable to build something but getting a livable wage as an indie game dev itself is a real challenge. Watch indie game the movie for reference on it. Chatgpt, even the free version can also quickly help you get up to speed to plan such kind of project. (Its also a huge autistic blessing to get an ai perspective on how your mails/messages can be interpreted and how you could interpret mails/messages from others.
Speaking as someone who has studied game development, i hope to make my own games aswell but purely as a hobby cause id be unrealistic to believe to get an income out of it. i could never accept a job in the industry where my talent is exploited for profit so even as a portfolio it wouldn’t do.