As it states in the title

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

pushing an end crystal with a piston into an end portal makes it teleport to the corresponding dimension

New behavior:

when pushing an end crystal into an end portal with a piston, 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 end crystals don't use in their tick.
Below is a screenshot of how the setup to replicate the issue looks, just power the piston and observe the crystal not teleporting: