You can break through end portals in survival mode by just pushing a sticky piston with a block through the end portal, lighting the portal and retracting the piston with the block back.

Steps to reproduce:

1. Craft the ender eyes;
2. Find a stronghold and it's portal;
3. Place a block of your choice in the middle of the lava box under the portal;
4. On top of that block, place a sticky piston facing up; (at this point, the sticky piston should be one single block under the portal)
5. Place a block of your choice (but no obsidian) on top of the sticky piston; (the block of your choice should be inside, in the center of the portal)
6. Activate the piston with a lever or some redstone; (the block of your choice should be pushed one block over the end portal)
7. Light the portal by putting all the eyes in the frames;
8. Retract the piston; (the block that was on the piston should retract, breaking through the portal)
9. Break the block that was retracted by the piston, which is currently inside the portal;

->  You broke through the end portal and now you got a hole in your end portal!

Video is kinda choppy but i think you can understand the issue from it.

Video: https://drive.google.com/file/d/1iSsg1h_dKEidGMMx1-ZDN2Fe9-iUif-v/view?usp=sharing