There is nothing like "ARM" in the market.

There is CPU/SoC X by Y, built on top of a license from ARM.

So you would have to boycott N companies instead of just AMD & Intel :( And even more so, since all their customers are EOM that are happy to sign NDAs.

There are ARM systems that don't need blobs. Whether they are useful to you is a different question. An example is the iMX line from NXP.