I’ve tried to replicate your issue on multiple computers and with multiple internet service providers and can not reproduce the errors you’re getting.
It’s possible that the github link you’re not able to access was down at the time you attempted. You might give it another go and see if it works a second time or a different time of day.
Are you on a office or school internet connection? If you’re still having trouble, the only thing I can think of is something on your internet connection is blocking access to github or another link in the JSON file that Arduino needs to access. You may need to try on a different network or from home.
It seems like when I mess with the files in the “arduino15” folder I can bring it up the “apollo3” boards, but I get another error from before from github not working correctly.
I cant seem to win.
These are the folders I have in my Arduino15 ; am I missing anything?
You should not need to mess with the files in Arduino15. Those are only for the Board Manager’s automatic operation. If you were to manually install the core you would do it in your Sketchbook folder. (there are many tutorials online about how to find that folder – it can be confusing at first depending on what platform you are using). It is possible to manually install the core but I don’t think you want that option except as a last resort.
Can you provide more information about the errors in your process? To best help you I would like to see you perform a fresh installation of Arduino and follow the steps in the guide while sharing screenshots along the way. Particularly important will be screenshots of any error that you get in entirety.