I'm not aware of a specific reference to the signing of minutes in the COVID legislation, but Paragraph 41 of Section 12 of the Local Government Act 1972 states that the minutes shall be signed "at the same or next suitable meeting" so there is leeway there to determine that the first face-to-face meeting is the next suitable meeting.
To avoid a backlog, I'm presenting minutes at every virtual meeting for approval, then arranging for them to be signed privately within a couple of days.