Keep in mind the Airy disk limit 1.22λ/d. Unless you're doing optical interferometry between satellites, 100mm resolution from 100km altitude, 1 microradian, requires an aperture about 800'000 wavelengths across. For blue light, that's a 300-mm-wide telescope; doable, although getting the optics to be that good is a serious challenge, motion blur is another issue, and such small sensor pixels don't get many photons and can be noisy. Now if you want to get to 10mm resolution, you need a 3-meter aperture; 1mm, like you're suggesting, requires 30 meters. These are much more challenging to launch.

There are some interesting things you can do with indirect light, but so far they don't help with this.

I saw something once that explained how the powerful magnification seems silly until you account for the angles that things are at.

The example they used was that license plates are vertical so to read them the satellite can't be directly above the car so it's actually a much further distance and greater magnification is necessary because of the atmosphere and the distortion of reading something at an angle.

Perhaps SAR with very high resolution too - allowing them to image at night and through cloud cover.

The picture Trump tweeted was from a satellite with a resolution of at least 4 inches. They can definitely see your cell phone, but they can't read it- at least not from space.