Following the previous thread about this (Tactix Delta Solar 'Cannot Unlock Maps') which has been closed (?), I have been in touch (as suggested by Garmin-Rob) with Product Support and I have been e-mailing back and forth, following up on the friendly suggestions, of which, amongst others, was installing Basecamp. Unfortunately this also did not solve the problem and the final call was 'wait for an updated version of Basecamp (Mac)'. OK. When will that be available? Apparently there will not be a new version of Basecamp, as the Basecamp team has been disbanded (https://forums.garmin.com/apps-software/mac-windows-software/f/basecamp-mac/282144/time-to-update-garmin-basecamp-for-macos)
So now what? Stuck with a problem, after months of forums, customer service, a lot of trial and error and no foreseeable solution. Instead of a valuable customer (owning a whole suite of Garmin hardware (Tactix Delta, Edge 1030 Plus, Rally RS200, Index S2 scale) and software (Garmin Express, Garmin Connect or Basecamp) Garmin is using us to trial and error the solution. I never experience this with any of my Apple hardware/software. No syncing issues, no strange messages. How difficult can this be, after all the user feedback I see on the various forums, to take this seriously and solve this @Garmin?