I'm sure most people who've ever said it were not talking about actual cases, only decoy reasons to get people worried about it and justify actions about it. But both things do exist: foreign backdoors (https://www.youtube.com/watch?v=lA8WuXDXfcI) and security vulnerabilities (too many router, smart TV, streaming box etc. botnets to count). Not to mention the backdoors and security vulnerabilities that aren't foreign (e.g. Tesla vehicles).

But I think both such things talked about in this announcement are complete bullshit, yes