Hey I am gonna do a thread of dragons you may have never heard of if you only been around since 5e and missing out on the deeper stuff of in the wide healthy arrangement of D&D dragon types.

First - Gem dragons which were often psionic dragons focused on inner elemental planes

The next type of "common" dragon would be your planar dragons that align with wherever they live. Everything from the Ethereal/Astral Dragon, shadow(fell) dragon, utterly insane Howling Dragons from the chaos planes, or Styx Dragons corrupted dragons bathed in the River Styx.

for the third type you have some very specific forms of dragons like the Lung Dragons that services the Celestial Bureaucracy pantheon. Or the horried Rust Dragon that would eat metals much like a rust monster living on Arechon.

A horried beast worth a mention all by itself is the Brainstealer Dragon which was a young wyrm that went through ceremorphosis. Often leading mind flayer colonies that did not have elder brains.

Less common ones were dragons of force, the 3 headed Dzalmus of the Hordelands in Faerun. The most mortally social Song Dragons loved to interact among the short-lived races. Rattelyr Dragon which often behaved like a rattle snake!

One of the more interesting intermixed species is the Dracosphinx which has all the riddle me this crap of a Sphinx and the mentality of a red dragon. Having the same breath attacks as a red dragon while being able to cast illusion spells setting it apart from either breed.

and the last batch I will be covering are Catastrophic Dragons which are Dragons that gave allegiance to Elemental Powers shifting them and merging with the host power. Everything from Landslides, wildfires, Tornados, and Typhons. They were everything and deadly.