Games that have either longevity or are the newest hottest trend tend to be the ones you want to look towards. Mobile games such as Marvel Contest of Champions, Raid Shadow Legends or Seven Deadly Sins already have a built in base of people today. That may change by the time you actually get started off in gaming. You can pay attention to the ones which are popular in the app store as an indictor. However, that is only part of the journey. Aside from picking a game which is popular, you also have to be good at it, AND enjoy it enough to want to play it regularly. One part of being a Youtuber is that you have to create a lot of content to keep viewers coming back.
Playing the video games are only 50% of the job. You also need knowledge in video editing/streaming, photo editing, marketing and pc devices and interfaces. A quick google search will get you a lot of information on the best platforms to use and equipment to invest in. I use OBS for streaming which is free.
Best of luck to you Tommy.
Here are some lists on the top YouTube games! I'd recommend trying a few out to see which ones you like best; perhaps pick a few from each list and you'll find your natural favorites. Enjoy!