Big Sur won't let me enter my keychain password

When I turn on my new iMac, which runs Big Sur, I get a prompt saying "accountsd wants to use the [name]-db password. Please enter the keychain password." I do remember the keychain password--it still works on my earlier iMac, which runs El Capitan--but when I try to enter it on my new iMac, I cannot. The characters are not echoed. I have to click Cancel two or three times to dismiss the request for my keychain password. How can I fix this problem?

I already checked that Keychain Autolock is off.