My background is backend development with Java and Kotlin for the last decade. I have a little bit of HTML/JS experience but I'm not a pro. I would like to build a modern Sierra game, of sorts.
I have no problem investing the time, it just seems overwhelming to jump into and while I've looked at a couple of tutorials, I still seem a bit mystified by the process.
I'm interested in multiplayer design and function twofold, as I'm intrigued at both how to make it work efficiently and the reasons some game companies claim their game servers cost millions a month to run and have to shut them off (looking at you, Gun Media).
I can only support this answer. Especially the official doc's are great.
I generally recommend not to blindly follow a tutorial. Instead think of your own little game (something of the scope that could be a mini game in Mario Party) and than divide it in small problems and start solving one after the other with the recourse mentioned above.
After finishing the first game your ready to make any game you want.
Agreed, hopefully since op has dev experience he learned that lesson long ago