No multiplayer access with 1.16.5 and above. Problems with entry with version 1.8 to premium servers and more

I bought minecraft from the original website on 06/18/2021 but I have a problem with accessing kokscraft, hypixel etc. servers in version 1.8. I am writing to me that we have failed to connect to the server, login failed: null. However, in version 1.16.5 and above, I cannot enter the multiplayer mode at all