I fully agree with
@Crown and
@markkaz here. YouTube is all you need to grow, short-term and long-term.
YT SEO still works. It's slow, grindy and feels like you're never getting anywhere with it, but it delivers a very consistent stream of new views every day, week and month. Viral effects never last for more than a week, maybe 2 and that's it, you're back at square one, so you have to have a solid foundation at the base. Master the biggest video platform and you probably won't ever need any other social media. It's good to diversify after a while, but no small YouTuber is in a position where they can even begin to think about something like that.
In the past, I linked to a few of my older videos on FB groups/pages and got a combined total of like 5 or 6 views from them, even though they have massive followings. After that, I didn't even bother. I never even bothered with Reddit either, I know from prior experience it's a massive time sink for a very lackluster result. A few relevant forums in my niche are cesspools of toxicity, egomania, gatekeeping and elitism, so I gave up on those too.
You have to figure out the specific combination of factors that work for your channel alone. Video topic matters a lot more than you think. The way you frame the topic is important too. Instead of titling your video "New Minecraft Character Models Review", it's probably better to say something like "WOW! These Newest Models Are Mindblowing", or something like that. It's still the same video, but now you're baiting the potential viewers harder to click on it. If you can target some trendy topic, do it.
Video structure and length are super important. They help keep the viewers watching, get good average view duration and stack dozens, hundreds of hours of watchtime. It's impossible to know what works for you. Vloggers get away with videos that last less than 5 minutes. For gamers, I think something in between 10-25 minutes is the optimal length range, but you have to test this for yourself to see.
Good thumbnail (anything above 10% CTR in my experience is "good") can literally make a difference of 100 views per hour or more if you can manage to get thousands of impressions from Homepage, snowballing your views and watchtime and making the video go "micro/mini/semi-viral". That means you have to test and experiment with everything, ruthlessly.
YouTube is in the business of keeping people watching videos on their platform so they can squeeze more ad revenue out of them. So, you have to try and do everything you can think of to make that possible.