A shulker in a minecart can not be affected by an entity or player. So the player can not push the cart when a shulker is in it nor does another minecart can push it.
Environment
Windows 10
Java: 8.0.2810.9
Minecraft snapshot 21w15a
A shulker in a minecart can not be affected by an entity or player. So the player can not push the cart when a shulker is in it nor does another minecart can push it.
Windows 10
Java: 8.0.2810.9
Minecraft snapshot 21w15a
Duplicate of MC-99097.