AMX instructions are available in EL0 yes, and are used by CoreML and Accelerate.framework.

A sample instruction: 20 12 20 00... which doesn't in any stretch parse as a valid arm64 instruction in the Arm specification.

Edit: Some other AMX combinations off-hand:

00 10 20 00

21 12 20 00

20 12 20 00

40 10 20 00