Go looking for second hand high school textbooks. For things like maths, chemistry, etc., these will include everything you're expected to know even if they're several years out of date. You might be behind on a few new discoveries but nothing important at the high school level.
Kahn Academy is a resource that I used to use with my students a lot. They're generally very good but I hear they're incorporating AI now so I can't guarantee they'll stay that way. They might do alright, or they might tank like Duolingo.
There are multiple youtube channels devoted to giving you a high school education. Crash Course is a good general one that covers a lot of basics, especially if you're in the USA. If it doesn't give you what you're looking for, shop around. There are so so many channels.
Unsure of what exactly a high school education entails? If you're out of high school then you should have a pretty good idea of what info you actually want or need to learn, but if you want the whole experience, go to your government's website and see what the Department of Education says. I can't give you a straight link here because it depends what country you're in, but your Dept of Education (or equivalent department, yours might have a different name) should have a national curriculum, or a link to a body that does have the national curriculum. For example, I live in Australia, where this is handled by ACARA, which tells me to find the Australian high school curriculum here.
