Not sure if this was present in other betas, but I find that if I pin a login from mini, that window is not actually in the foreground, so I can't select any text from something like the Notes field in order to copy. If I right click on the text there and then deselect it, it seems to get that window into the foreground and then I can select text.
1Password Version: 7.3.1.BETA-4 (70301004)
Extension Version: Not Provided
OS Version: 10.14.5
Sync Type: Not Provided