from what I understand, not all webbrowsers work with GLES3. you can easily set this to GLES2 in Godot (top right corner). it will ask you to save and restart to change your project to GLES2. this way it will work in all browsers, but some things will no longer work. GLI-probe and particle system are not working in GLES2, probably other things also. if you set your project to GLES2 but don't like the outcome you can set it back to GLES3 the same way you changed to GLES2. this is only for HTML5 exports, and Godot 4.0 will probably fix this.