>>>>>>Can you please elaborate what clipboard manager is

Clipboard manager is an application that adds functionality to an operating system's clipboard:

https://en.wikipedia.org/wiki/Clipboard_manager

Here are some examples:

https://www.slant.co/topics/2622/~best-clipboard-managers-for-mac

>>>>>Why is everything I paste become a pasteblock?

The default OOTB shortcut for PASTEBLOCK command is Shift+Cmd+V, not sure why it is Cmd+V on your side.

From your last answer I still don't get  - is your "paste problem" resolved?

BTW - have you installed the latest Update for AC 2021 for Mac? I resolves some issues with macOS Big Sur:

AutoCAD for Mac 2021.1.1 Hotfix