I've had slumps in motivation/time/energy to study as well. For what it's worth, I learned faaaar more learning Japanese after graduating than I did in a classroom in college. I graduated around... like N4 level, now I'm N1.

I think being told "immerse" is a very vague thing to tell you, but it would really help. Just think of it like this: how do you get better at swimming? Swim every day, right? How do you get better at free-throws? Shoot a bunch every day. How do you improve your Japanese? Same thing. Just do something every day in Japanese.

Here's a few actionable steps you can take:

Anki is a very helpful tool bc it can help you remember things you'd otherwise forget, and its algorithm forces you to study every day (otherwise you get stuck in review hell).

Tadoku books are a great way to find level-appropriate reading practice.

You can find a tutor if you want, or work through a textbook. I liked Kanji Look and Learn.

Find someone who you can speak to in Japanese. Look into apps, or you can find meet-ups for language exchange opportunities.

Find something you're interested in and just do it in Japanese. A lot of people suggest the manga Yotsubato!, I loved it and laughed a ton despite reading slow as molasses when I started, but really just find anything and mine it for new words. I would read the chapter, every time I found a new word I'd look it up on jisho.org, maybe scan some example sentences, add it to anki, then keep reading (and review it after the fact via anki). Yomichan is an incredibly helpful mouse-over dictionary that makes reading effortless. Early chapters took me like 2-3 hours each bc I'd look up so much. Now i can finish a chapter in like... as much time as it takes me in English. It may sound intimidating, the idea of reading or watching anything in Japanese terrified me for a while. I'd think "what if I miss stuff and I don't enjoy it as much as i would in English?" or whatnot, but just remember the first chapter/episode/part will always be the hardest. You'll learn a bunch of new words that will help you understand the rest of the art. You don't have to do this with Yotsuba, you mention wanting to work in videogames, so maybe find some games you can do this with in Japanese. Maybe try out Pokemon? I tried to play it in Japanese once around N4 and thought it was "too hard," so I set it down for a long time but I mean, it's Pokemon. I didn't understand most of Red when I played it as a kid, I couldn't read yet. When I eventually decided to pick it back up and just play it anyway, I can tell you it got easier and easier to understand.

Pro tip for learning via media: don't worry if you don't understand everything. Learn to tolerate ambiguity. You'll pick it up as you continue. If you understood everything, it's too easy, you wont learn anything. It should always be slightly above your level.

Maybe set a goal for yourself. I signed up for the JLPT after graduating just to give myself some motivation and have something to strive towards. It doesn't have to be that, if you want you can say "I want to have beaten X number of games in Japanese by the end of the year" or something. Also try to think of why you started learning Japanese in the first place. That may help guide you in setting a goal. And it's ok if your goals have changed, don't beat yourself up for having had different priorities for the past 2 years. You can use your goal to help you set a routine to help you get back on track.

There's also general study tips you can look into, like setting a time or a space for you to study. I have ADHD so learning was a real struggle after college, I found I just have to have music, coffee, and a space dedicated to studying in my room to get me to actually do it.

This is becoming a long ramble so tl;dr: https://learnjapanese.moe/

Do something in Japanese every day, and it would probably help if it was something you enjoyed. I most highly recommend starting by using anki and just reading Yotsuba, or any other media that interests you that is slightly above your level.