I also present the CEO and board with other arguments, like moral ones about involvement in atrocities and tyranny, legal ones regarding things like data protection, market related ones such as the likelihood of a future showdown between the EU and US.
But the risk that MICROS~1 fucks us over directly is even easier for them to understand, because they have been using Windows and Office for decades and are quite queasy about 10 going EOL and what the next set of annoyances in document management will be that they'll have to suffer under. It's something they have immediate experience of and didn't like.
A year from now it's probable we'll only have a couple of Windows machines left, because some of our customers use software that doesn't run under Wine and tries to block execution under both debuggers and container environments.