Thank you for the EtreCheck steer. It identified a Dropbox file as unsigned, then I found Dropbox in the Login Items again and deleted it.

I am now back to a 30-second boot.

Cheers!


iMac (19,1, 3.1 GHz i5, 12.7.4, 40 Gb RAM); MacBook Air (1.8 Ghz, 8 Gb RAM, 10.14.6, 256 Gb SSD) Vodafone router and Devolo Wi-Fi Extender, Canon TS8351 printer/scanner.