Trump would be anti-TikTok if it was elderly anti-Trumpers using it. He's not capable of deep thinking, but he's more your inadequate kid in the sandpit grabbing toys of others who are calling him names.
Regard him as a cranky toddler and he's pretty easily understood.
It may also be that Sarah Cooper who mocks him using his own words is most visible on TikTok. He sees taking action against TikTok as harming her.
But hey, turn to Twitter to mount up your militia. That's one platform he's not going to touch.