The fact you’ve made it here onto the fediverse suggests you’re pretty tech savvy. Have you considered offering tech support services locally? There’s probably loads of older folk around who would appreciate someone who can sort out their laptop, set up their printer etc.

You could also try a specific subset of this if you wanted to optimise for reputation and cash - e.g. Get good at setting up mesh wifi systems like Amazon Eero and then sell your services locally as an installer?

None of my business, but maybe you should focus on what’s causing you to fail in school first. I get that it’s the summer, now, and there’s no classes, but if there’s certain subjects you’re falling behind in, there’s resources online to get caught up in those subjects before the fall. What’s your situation? Maybe I can offer some advice.

You could hold a yard sale and try to sell your stuff, but you should talk to your parents first, because… they might not appreciate that.

Depending on how old you are, there might be businesses offering part time work over the summer. What the age limit for that is, and what additional requirements there are, will vary based on where you live.

Do you have any potentially marketable skills? For example, web development for small businesses is something you could potentially offer that would pay better than yard work and generally be less tiring.

First off, do what you can to not fail out of high school. The job market can be tough, it’ll be even tougher with no diploma.

As for money, I’d recommend flipping items on marketplace / Facebook. Lots of people out perfectly serviceable furniture, appliances, and electronics that may need small repairs or a good deep cleaning. If you have a vehicle, that might be a good source of some income.