How can I tell if a dimmer switch is LED compatible?
As a general rule:


Incandescent bulbs - will dim with any dimmer
Fluorescent bulbs - require a dimmer-compatible bulb and a compatible dimmer
"Simple" LED bulbs/fixtures (i.e., not much difference whether fixture + bulb or "all in one") - require a dimmer-compatible bulb/fixture and a compatible dimmer
"Smart" LED bulbs/fixtures (and technically speaking, smart "any" bulb or fixture, but normally only found with LEDs for a number of technical &amp; economic reasons that are irrelevant at the moment) - normally require "full" power and any dimming will be handled inside the bulb/fixture.


In addition, as Harper pointed out, there are certain locations (especially stairwells for obvious reasons, but also in general "one per room") where there is an expectation, and code requirement, for a light switch to function to turn lights on/off (unless you just leave lights on all the time - which is practical in some situations). The catch is that if you use an ordinary switch with a smart bulb *and the bulb defaults to "off" when power is initially applied, or remembers previous setting, even if that was "off") then you could end up with the following situation:


Person A turns on switch and then turns on light to desired setting via an App or remote control.
Person B turns off light via switch - no power = no light.
Person C walks in (at night) and turns on switch - and nothing happens. And trips over the remote control that A left on the floor (or whatever...)


This is not a problem with:


Secondary lights - e.g., ceiling light has a regular switch (or a permanently installed wall smart switch) and the smart bulbs are in table or floor lamps as an additional source of light
Smart bulb defaults to "on" after any full power cycle (this may indeed be the default on some (many? all?) smart bulbs, but it is critical for safe operation if the smart bulbs are the only light on the primary switched circuit.
Wall switch is itself a functional remote for the smart bulbs.