If I work with someone (supervising or not) I know if they are working or slacking off. And no, you don't need made up metrics or to be sitting next to them for that. If you really are in the midst of people that actually get stuff done, I should add.
On somewhat of a tangent, I'm not gonna lie: it sometimes feels like everything is a big farce in tech.
We write code for useless functionalities on mostly useless products. Product managers often don't even understand/use the product and copy competitors blindly. C-suite/founders pretend they know what they're doing but copy whatever is trending at the time (Agile, OKRs, Scrum, squads, etc). Investors give out money to people that yell the right buzzwords loud enough (and/or have the right connections). The list goes on.
The only people that really work are the ones in the lower echelons answering support tickets, keeping things running, actually committing code, etc. Everyone else sits on useless meetings adding "meeting for X" in their reports. Ironically those getting things done are the most scrutinized for "LARPing" by higher ups.
Maybe I've been really unlucky in my career but I've found this to be true in every single job.