Boos are only justified when a performance is shockingly bad at a time when the team are performing way below expectations on the pitch, such as yesterday. In which case, everyone shares criticism, but the manager has to bare most responsibility.
I don't think the performance was 'shockingly bad' other than for the ref and VAR. We were in control of that match and could have been 3 or 4 nil up until VAR decided to take control. Xhaka can also be blamed for the cross coming in for the equalizer for what it's worth...but let's remember, the booing only started after he started trudging off - at a time when we needed to get a move on. For what it's worth the fans had been booing since before half-time over their time-wasting, yet here you have your captain doing just that.