Will data be lost in resetting macOS admin password?
As you mentioned, credentials will be lost including the Keychain, but files will be preserved. You can either create a new account, log into it and change the permissions on the original account’s home folder to be able to access the files, or reset the password to the existing administrator account and log into that. The former will preserve the Keychain in case the password is recovered while still giving access to the files.