What is the little orange triangle on some of my plugins?

This is an I/O -configuration warning.
If this icon is visible on a plugin in a chain, it means that the plugin could not support the same input/output configuration as specified by the chain

When you add a plugin to a chain the plugin should adapt to match the channel configuration of the chain. But some plugins can´t do this, and the triangle then warns the user that there is a mismatch.

This could be the case if you have a surround-only plugin added to a stereo chain or a mono plugin in a stereo chain.

In most cases, this will play just fine, but the plugin might not process all the channels as expected.