This lawsuit look specious.
I work in the industry. A.good engineers needs only take himself/herself. I can recreate anything I have designed. If I do it a second time, it will actually be better because I won't make the same design mistakes.
The company is making a RiscV processor not ARM. While some techniques and architectural elements are portable the architecture and instruction set are completely different and you just can't slap stuff from an ARM processor into a RiscV.
Companies do this kind of lawsuit to prevent an employee from going to a perceived competitor. There is nothing about a RiscV that makes it competition to Apple