"Read only" on Macintosh HD and External hard drive

Hello, i just want to know how to fix this issue. I checked my folders and all have "read and write" permissions and I can see my name (Administrator) on the list. But when I go to Macintosh HD, not only that my name (Administrator) is not visible, it says "Read only" under sharing and permissions.

Also, I have used my external hard drive until last week to save files, so i know its on the correct format for mac. Under Sharing and Permissions, on my name (Administrator) it says "Read and Write". But its not letting me save files on it.

Note I just updated to Catalina last April 2020.

Are these two issues related?

Thanks.