Editor GameView locked at 60 fps on new project

I create a new project. I set Edit->Project Settings->Quality->Vsync Count = 0. I build and run, profiler reports ~1000fps.

I create a new script and add it to the camera:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;

 public class Vsync : MonoBehaviour
 {
     void Start()
     {
         Application.targetFrameRate = 300;
         UnityEngine.QualitySettings.vSyncCount = 0;
     }

     void Update()
     {
         Debug.Log(Application.targetFrameRate + " " + UnityEngine.QualitySettings.vSyncCount);
     }
 }

I create a new display resolution for the Game tab and set it to 10x10.

I click play and turn on stats, fps initially spikes then settles at 60+-0.1. Console reports targetFrameRate as 300 and vSyncCount as 0.

I turn on profiler, 92% editorloop. Change to editor profiler, update rendering is main culprit, see image.

Have tried with 2020.3.33f1 and 2021.3.3f1. Am using linux mint 20.3 Cinnamon, kernel 5.13.0-39, Ryzen 2700x, asus RX 480x 8GB.

I code for fun, have spent 6+ hours trying to sort this and feel utterly defeated. Any comments would be incredibly welcome, a solution even more so.