Elves and Gnomes can choose an ancestry feat that gives them a cantrip as an "innate spell", which "heightened to a spell level equal to half your level
rounded up".
Let's say I'm playing an elf fighter with this feat and I take acid splash. At 6th level, I decide to take Wizard Dedication, and get a spellbook with 4 "regular" spell cantrips.
At this point my innate acid splash is heightened to 3rd level. Because I can cast this spell at 3rd level, are my other cantrips also heightened to 3rd level?
Cantrips are always cast at a spell level of half your character level, rounded up, regardless of where you get them from.
It looks like cantrips always scale at the same rate (though I may be missing the exception somewhere) p. 193 says that if you can cast cantrips but no spell slots it scales at half your character level just like the gnome primal cantrip.
So that whole spell slot line seems unnecessary since all characters without spell slots scale at 1/2 lvl, all full casters have a highest spell slot progression that matches, and then for the archetype wizard and cleric where you might expect that rule to matter they have language that dismisses it.