I hate to suggest this, and a lot of people will look down on it, but you MIGHT consider using an AI generator for things like thumbnails
Check out this site, it will allow you to make some content for free every day, and after a limit it will charge:
https://hotpot.ai/art-generator
AI is kind of a hot topic because of the social ramifications of people losing their jobs, but for someone like you just trying to get started and build an audience I don’t think it’s a great Idea to be sinking money into it just yet, you should be focusing on your videos and getting them out there and all that!
I more than respect if you’re against AI generated art and thumbnails, but the genie is already out of the bottle and a great many VERY succsful youtubers even in this sphere use it all the time.