As it states in the title

Old behavior (can be observer in any version before 24w21a):

dropping a tnt into an end portal makes it teleport to the corresponding dimension

New behavior:

when dropping a tnt into an end portal, it wont teleport

This happens due to the change in how end portals are processed, before the change they teleported entities instantly upon collision and now they require entities to perform handlePortal() method which tnt doesn't use in its tick.