I would hate to be a stakeholder in a company whose value depends on employees not talking about and reusing the incremental skills and knowledge gained while working there.
I don't think knowledge on any particular api is particularly useful compare to the more generic "can you read docs and use apis" skill, which is directly applicable from something like high level hard ware work making an ftdi USB chip go brrr to making dynamoDB work nicely, but I definitely didn't know anything about dynamodb before doing a server/web job
Async distributed systems and FPGA vhdl have some overlap in how you build things, but doing an interview based on my old FPGA skills likely won't show much of my servers and databases systems design skills
If platform X is something public, they could talk about the platform. But, talking about any project specifics, implementation details, etc would be a felony.