Conversely, I had to attend more meetings when I didn't have a manager, because they were no longer there to act as a filter/shield for the chaff around the corn of what I needed to know.

What do you need to know from your manager exactly? Majority of my assigned work is coming from my project lead.

Presumably someone was still managing you (e.g. there was someone for you to go to if you wanted to book time off, ask for a pay rise, etc)?

Vacations are booked through a booking system, pay raises are negotiated by a union, so not an issue.

Mind if I ask where you’re from? Even in highly unionized Scandinavia I’ve never seen software devs (specifically) join unions to any larger extent, let alone negotiate salary through them.