Android SDK is invalid

Hello,
I wanted to install unity on an older PC with a Windows 10. Fist it worked but the android sdk was invalid. Then i tried to reinstall this version (2020.1.16) but the hub printed out an installing error. After that i tried to install unity via the archive without the hub. This worked but again the android sdk was invalid.
Please help me.

Sorry for my bad english

problem fixed here : Unity Android SDK not found | android sdk not found or invalid unity - YouTube