1. My manager in particular would never do that, but even if they did:
2. I know how much I contribute relative to my team. If my manager told me I was underperforming - for any stated reason, but especially if I suspected it was for taking "too much" PTO - I'd almost certainly find a new team, because that just ain't so.
To elaborate on 2 a little bit, it's worth pointing out that you're definitely more vulnerable to shitty management tactics like that if you aren't sure of your own market value.
If your main point is that "unlimited PTO" can be a weapon in the hands of a bad manager, I concede that. But my counterpoint to "unlimited PTO is bad" is that, within the bubble world of tech, we as employees have so much power to dictate our working conditions there's very little reason to put up with any such bullshit in the first place. And most employers are aware of this right now.[0]
[0] https://www.sandiegouniontribune.com/business/story/2021-07-...