The only solution I can think of for this exact scenario is, unfortunately, a bit more complicated than you might prefer. The boolean solution you're describing can be extended to work for individual users with a helper entity. There are a number of ways to work out the details but they all involve an entity with a single boolean attribute and associations to both the template grid object and the current user. Then you need to make sure that your click microflow retrieves or creates the correct helper object and toggles that boolean.
This will probably involve some superfluously complex microflows and the aforementioned extra entity, so you'll have to decide for yourself if you feel this feature is worth the added confusion while debugging in the future.
PS. Accents on vowels for emphasis (like in your title) don't work in English, you should consider using italics in the future :)
Hey there, I think there is a better solution:
We had the same situation, where an association was set, and we wanted to use single click to do so, but also maintain selected.
The trick is this: we duplicated the row-data, and applied the class “selected” to the top one, with conditional visibility: if the current object is the same as the one in the association, show this row. For the bottom row, we used the inverse: not(theConditionListedAbove).
For us, it worked like a charm!
Hope this helps!