LauraNorder I too am in favour of a United Kingdom. The slogan was "better together" and it was a true one. It is better that the various parts of the kingdom are united and work together in things like import/export and social and working conditions for the prosperity of the whole.
However, each region has its own personality, needs and priorities. That was recognised when Wales and Scotland devolved to have their own Parliaments responsible for various internal matters, getting a fair proportion of what is spent on those matters over the whole country and contributing a fair share from the taxes paid in Wales or Scotland. (Those moaning about Scotland using some of that money for prescriptions should lobby Westminster to do the same in England)
Health is of those devolved issues. Decisions on combatting Covid some under the health umbrella. The four countries of the United Kingdom can discuss Covid measures, and pass on ideas and experiences, but the decisions are still up to the devolved Parliaments. Johnson has no authority to apply pressure for everything to be exactly the same - the same as Westminster!
This visit is a political one, at a time when Johnson's popularity level is sinking like a stone. He thinks he can bump up his appeal by being masterful with Nicola Sturgeon. You don't have to be an SNP voter wishing for independence to know that he is likely to come off worst in that encounter.