"Downloading installer information to the target volume failed" when I try to update my iMac

My iMac is currently running version 10.13.6 and I'm trying to update it to Catalina but every time I've attempted to download it through the App Store I just get a message that says "downloading installer information to the target volume failed". If I download the update from apple's site it tells me that I need 10.15 to update, which is obviously a problem because I can't find or download it.

I've googled this and tried to find help. People have said to use another admin account and that didn't work. Others have said to boot into safe mode and I've attempted this but it wouldn't work for some reason. I don't know if it's because I'm using a keyboard that isn't from Apple or if it's just another unidentified problem my computer is having.

If anyone has a fix for this please let me know because I need to get my computer updated.