Though I have asked a similar question here, and I am very thankful for NautArch's answer, I realized that the more I looked into the text of a changeling's shapeshifter trait, the more questions I had as I am not quite understanding their limitations and specifications.
To reiterate the text:
As an action, you can change your appearance and your voice. You determine the specifics of the changes, including your coloration, hair length, and sex. You can also adjust your height and weight, but not so much that your size changes. You can make yourself appear as a member of another race, though none of your game statistics change. You can’t duplicate the appearance of a creature you’ve never seen, and you must adopt a form that has the same basic arrangement of limbs that you have. Your clothing and equipment aren’t changed by this trait.
The first part of the confusion I have is knowing what exactly you can change into. Adjusting height, weight, color, (gender, hair length), and race so long as they are a medium creature sounds simple enough, but does this mean you can be any creature with 4 limbs in a medium-size? From a medium minotaur to a wolf? From a Babau to an animated armor? What about see-through creatures like Shadows?
The second part of the confusion is understanding the nuances of how sizing works. While I realize that the basic rules focus on player space, I found that the System Reference Document of 3.5e seemed to comply with 5e's guide when checking playable race height guides, so good as a guide to find out how tall/short I can make my changeling.
According to that, a changeling can be anywhere from a 4ft 60lbs character to one of 8ft and 500lbs. However, as a changeling's stats don't change and things like speed and lifting strength are not tied into the size of a creature, does this mean that your changeling monk with the mobile feat and a +1 strength (for instance) could appear to be a 4' dwarf weighing 60lbs carrying 225lbs at 60ft per round the same as an 8' tall goliath with 500lbs of pure muscle unable to do any better?
I realize that these examples might seem exaggerated, or quite different, but there are there to highlight the confusion that I still have with the changeling's feature; the monster type is described in 3 vague ways (descriptors, race, creature) leaving little understanding to the limitations, the stats remaining the same seem odd if one can gain or lose muscle mass, and I can't seem to wrap my head around it.
Last note, I realize this question is quite similar, but I am still confused and was hoping for a bit of clarification.