John Deere, broadcom, Cisco, many more examples I can't think of now.

Broadcom are actually one of the most well known assholes for this, well before all these Chinese companies appeared.

Also in the Xiaomi case it's not strictly on purpose as they do release sources, they just don't want to or can't allocate resources to doing something that generates no revenue whereas broadcom for example have stated they are just refusing because they don't want to and nobody can make them (which thus far is true, they've won cases before under the guise of it disclosing IP) - now they can just claim the Chinese will steal their IP and disadvantage America so nobody will do a thing.