I currently make 40 tickets, perhaps I associate with an activity as there is a "parent activity" option. Once this is done, it's not visually apparent that 40 tickets among maybe 200 are linked to an activity.

For sure, this is not easy 🙁

If I visit the parent activity, likewise, I cannot see there are a large number of tickets associated. To remedy this, a user must link elements manually from ticket or from activity with the vice versa.

No, linking is not, imo, the good solution.
Another way, with existing version, is to set a filter "Activity=your activity", then you'll easily find the tickets.

It would be good if:
- When setting a tickets parent activity, the activity gains a linked element

No, linking is not, imo, the good solution.

I'm aware handling needs to be in place for changing the parent activity (causing loss of link on old parent)
What's your thoughts?

I recorded Ticket #1310
Maybe best way is to provide some pop-up to show Tickets list...

I recorded Ticket #1310
Maybe best way is to provide some pop-up to show Tickets list...

+1 for Tickets list