Afaik, webgl has failed to support compute shaders (and instancing for that matter) since 2017.x, even with the Graphics API setting set to webgl 2.0 in the player settings. Issue related to this was reported here and was marked “Wont Fix”. Even if it contradicts with the user manual here.
Not sure “failed” is more correct than not wasting time and money since compute shader support in browsers is crappy at best, if it actually works. WebGPU is also under development.