First and foremost, the reality is that there is a lot of tutorials that are both still good for modern GM, that are quite old (older than 5 years). But, moving on from that, we do have some newer resources for a couple of things, just more in writing.
I'm going to tackle the more networking side rather than gui/player data/mobile for the moment, since those problems are usually more trivial and can be figured out with just most existing tutorials, resources or some trial and error. (I also would recommend just getting networking done as soon as possible, because the sooner that's implemented, the easier it is to make changes down the line.)
The first consideration is what platforms you intend to be played on. I can assume Desktop (Windows) and Mobile (iOS, Android) are your main targets. But if you do actually want it hosted via a website like GX.games or itch.io or wherever, then you are limited to using Websockets with GameMaker. (And I would at the very least recommend just using the GX.games target. That can both run JS extensions & can be exported as a local zip and uploaded anywhere, including calling GML functionality from the JS side. Just like HTML5 target, but way better.) But most importantly, when it comes to making your packets, use JSON for those. Easier to debug networking that way.
The second consideration is that you would ideally want to try to at least get a server host for you to host a developer server of some kind, and a production server down the line. Now, the developer server doesn't need to be actually that fancy. GameMaker out of the box doesn't need much RAM, and you can easily afford a Linux server for as low as $5 USD/month. (which yes, you should be able to build & deploy to Linux at the very least.) There is some other catches with running on Linux, but for the most part, you can run a server completely headless with little to no difficulty. (There might be actually some resources to help with this, but any host that can host Ubuntu Linux (ideally for compatibility sake) w/ GameMakers required dependencies and can install xvfb, is all you need.)
Those are at least the very basics, and in some setups, you may prefer some kind of automation so the developer client & server can be built and deployed automatically, but that is a separate matter.
Assuming you have those two covered, and you've got a relatively playable networking game, the next thing is covering player data. Which for the most part, we do usually recommend JSON. And we have dozens of tutorials on those. But for a multiplayer game w/ logins and all that, you would ideally want some kind of database system. Outside of Firebase, the only other option is writing either a separate server, extension or using HTTP, that can integrate with SQLlite, MySQL or another database software, in some way. GameMaker can communicate with almost any service out, even to servers that aren't built in GameMaker. (Though you do at least want the main game server to be in GameMaker, because replicating GameMakers systems in another language sucks, and GameMaker does very well even for an MMO.)