ASTC is a hardware compression format for textures in WebGPU and WebGL.

The problem is that it is implemented in hardware which is kinda orhtogonal to the browser version. Not sure if it can be added at all.

But anyway to track it you'll need to create webgl2 context, request an extension called WEBGL_compressed_texture_astc, and then call getSupportedProfiles() on the extension. It will return an array with one or two strings. One of which will probably be "ldr", and another "hdr". So if hdr is present - it means that hdr profile is supported.