Iris

Iris supports all versions 1.16.5 and higher. Versions that do not appear in the installer were likely removed due to the next release being compatible with servers of that version.

Iris supports Fabric on 1.16.5 and higher, and NeoForge on 1.21.1 and higher. Forge is not supported.

Iris aims for broad compatibility, however, some shaders may not support some devices. If you believe a shader not loading is due to an issue in Iris, please join our Discord. Otherwise, please contact the shader developer.

Most mods work with Iris. Here are a list of some mods that change rendering that may have trouble.

Nvidium: Will disable itself with shaders enabled, but can be installed with Iris.
Voxy and Distant Horizons: Compatible with *some* shader packs. Shader packs must explicitly support them.
Optifine, Canvas, or Vulkan mods: Incompatible, and will crash the game.
Indium: if below 1.21.1, yes. Indium should not be used on 1.21.1 and higher.

Hacked clients (Meteor, Wurst) are not supported.
Non-hacked clients, such as Lunar Client, may have support from their respective team; but you must contact them for any issues exclusive to it.

Most texture packs will just work, yes. Resource packs that use "core shaders" (shaders that do not require mods) will not work with a shader pack enabled.

No.

Serious answer: Bedrock Edition cannot be modded due to restrictions on mobile devices. Any shader mod for Bedrock Edition on mobile that does not use it's built in features is a scam. (Though, if you're on Windows, you can check out BetterRTX!)

I could not care less. You're still not getting support.