Ran sudo apt update and shows errors

Assuming that you ARE running Ubuntu 21.04...

Note: Your system may not have updated/upgraded properly in the past.

Note: If you have any difficulties with these instructions, stop, and ask for help.

Edit two files...

sudo -H gedit /etc/apt/sources.list

deb http://us.archive.ubuntu.com/ubuntu/ hirsute main universe restricted multiverse
deb http://archive.canonical.com/ubuntu hirsute partner

Change bionic to hirsute like shown in the above two lines.

Save the file and quit gedit.

sudo -H gedit /etc/apt/sources.list.d/dropbox.list

deb http://linux.dropbox.com/ubuntu disco main

Change eoan to disco like shown in the above line.

Save the file and quit gedit.

sudo apt update