Can't open Keychain OR get rid of "accountsd wants to use the "login" keychain." + other similar messages in High Sierra

Safe Boot, (holding Shift key down at startup), does the problem occur in Safe Mode? Could take 10 minutes.

Safe mode attempts to repair Disks & clears lots of caches & loads safe Drivers, & prevents loading of 3rd party extensions, so if Safe Mode works try again in regular boot.

Accountsd asking you often…

Just open the "Keychain Access", click right on the "login" keychain in the sidebar, select "Change settings for Keychain "login"" and unselect both options "Lock after ..." and "Lock when sleeping". – Tom Kraina Sep 8 '16 at 10:55

If your Mac keeps asking for the login keychain password

The password of your macOS user account might not match the password of your login keychain. Either create a new login keychain or update it with your new password.

https://support.apple.com/en-us/HT201609#:~:text=Either%20create%20a%20new%20login,password%20of%20your%20login%20keychain.