I wrote the initial .opvault import into KeePassXC and briefly considered going after their local .com cache file
(hidden in a very obtuse place, of course) since it seems to be using their same opdata01 <
https://support.1password.com/cs/opvault-design/#opdata01> encoding, at least when last I looked, but then suspected that the audience who would have already paid for 1P but wanted to switch would use 1PUX. Seems maybe that does need more consideration
$ cd ~/Library/Group Containers/2BUA8C4S2C.com.1password/Library/Application Support/1Password/Data
$ sqlite3 -readonly 1password.sqlite
sqlite> .tables
account_objects creation_drafts item_overviews ssh_pubkeys
accounts deleted_accounts item_usage users
autofill editing_drafts kanon_autofill
collection_map feature_flags objects
config item_details search_weighting