OpenGL ES 3.1 does not require multisampling to be supported on integer texture formats. The minimum value for GL_MAX_INTEGER_SAMPLES is 1, and 94.7% of reports on gpuinfo have that value: https://opengles.gpuinfo.org/displaycapability.php?name=GL_MAX_INTEGER_SAMPLES&esversion=31

There are per-format queries that may indicate support for integer formats on some devices, but there are no GL spec requirements for them to do so. I don't have a source for per-format queries at the moment. One device that we know does not support integer format multisampling is Pixel 6. Although this is not a target for Compatibility Mode, it does not bode well for older Mali devices.