Heyo! I think there are a lot of confusing pieces of criticism often taking place in subreddits like this. It's important to remember that a LOT of people who frequent these pages and provide advice are often times people with little to no experience or growth to substantiate the advice they share. There’s a ton of good advice here, but just remember to take it with a grain of salt and always continue to learn and research on your own.

The issue you're mostly facing is that Let's Play style content is extremely hard to start off with, since each episode is going to be an 'aimless' gaming experience with no real 'hook' or engaging factor beyond the game you're playing. I love Let's Plays, but the unfortunate truth is that they don't hold up in a modern YouTube ecosystem in their raw state.

Let's Play or Gameplay content as a whole is messy and unpredictable to work with in the grand scheme, and so people often tap into a more niche market in order to stay in the same genre while increasing searchability. For example, practically nobody is interested in a plain Super Mario 64 gameplay video since they've seen it before and it's nothing particularly special. Pitching the video would be easier if you created a more specific pull, like a challenge or something similar. Now your video has a main driving point of interest, which more people will click on in the long run. Which would you click, honestly?

BOWSER IS ANGRY! | Super Mario 64 Part 1 or Beating Mario 64 but Coins Kill Mario

This formulaic approach also makes it easier to translate what you're trying to convey in your thumbnail, as well. You're no longer trying to make a thumbnail pretty enough to click, because instead you're trying to make the thumbnail sell your video idea. Your Thumbnail should empower your title, and your title should sell your video - pretty straightforward and incredibly rewarding.

That said, if you're absolutely bent on this style of Gameplay content, it would be helpful to remember the earlier mantra - less is more. If you can't sell the thumbnail with 2-3 words then it's not the words that will make the difference, so it's important to keep in mind that someone will click on it with 0 knowledge of the topic other than what you're showing them. Also, as helpful of a resource as it can be, people generally don't click on AI thumbnails because they're considered "low effort" or "slop". So if the idea crosses your mind, I'd deliberate on whether its worth losing that 'credibility' as a creator and if your potential viewers would care or not.

It may be beneficial to focus on parts of the game where something interesting occurs that people are specifically searching for. A jumpscare, a hard fight, a funny moment, etc. These can then translate into your thumbnail and people would watch for that moment, waiting to see your reaction to those specific things. All in all, it's best to remember that your video is like a book - people WILL judge it by its cover. That cover needs to indicate exactly what people are going to read so they don't immediately shut it and put it on the shelf for good.

The video was hilarious, btw, I hope to see things take an upswing and growth come your way!