I did some further searching and experimenting. I found a reddit thread which talked about moving passwords. If I export the passwords on the original machine (which creates an unencrypted .csv file - not cool) and then import them into brave on the new machine that works. Except that the import process “deletes” the .csv file. I would rather wipe it securely.
This makes me think that Brave is using something related to the machine it is installed on to salt the encryption of the passwords. This might be good from a security standpoint but it raises issues re. backup. Do I need to routinely dump passwords to a plain text file as part of my backup process? Not cool.
Thanks also for the tip about the password manager. I do need to select one some day.