Some time ago, like in 2021, I discovered this Morph class from EN World's A Touch of Class document on 5E SRD licensed to be put on the website by EN Publishing themselves.

https://www.5esrd.com/classes/3rd-party-publisher-classes/en-publishing/morph/

"Morphs are the embodiment of transformation. Whereas a druid looks at the power of beasts as just one weapon in their arsenal, the forms morph characters take are the core of their being. Each morph has an exceptional degree of versatility in adventuring, because they could as easily become a rat, wolf, or monkey to resolve the situation at hand. Furthermore, each morph has forms (and problemsolving strategies) they prefer."

"Why hide when you can become a rat?"

"Why cast spider climb when you can become a spider?"

"Why don a disguise when you can simply assume a new identity?"

It looks like a cool shapeshifting class for fifth edition D&D, similar in scope of the Master of Many Forms prestige class from D&D version 3.5. You don't get spells with this class so it is definitely more focused on shapeshifting than the Druid's Circle of the Moon subclass.

The class description starts by saying that each Morph gained the ability to change into other forms as a result of an incredible experience of some kind. Reasons it suggests your character could have gotten this ability include your character getting "blessed" by a fey creature or cursed by an aberration, a horrible event like a failed arcane experiment or shattering of identity, or your character beginning training to be a Druid but focusing far more on the shapeshifting element, possibly to the point of not properly being initiated as a Druid.

You choose between one of three subclasses when you acquire this class, choosing between the Doppleganger, the Primordial Beast, or the Trickster essences, which while only giving you a feature at level 1 and level 17, some traits you can choose from require a specific essence.

The class has a talent system in which you can pick and choose some aspects of the class to acquire, up to eight at level 18. The Ancestral Beast trait allows for using the Natural Weapons acquired from the Primordial Beast while shapeshifted, more of them in general, and to pull them out all at once with an action, useful for feeling more like a chimeric creature. All-Terrain Physiology, available at class 15th level and higher, allows you to cast Alter Self at will for no spell slots similarly to Druids from the Circle of the Moon. Some traits allow you to change into additional forms by using two uses of shapeshift. Tiny Changeling allows for shapeshifting into anything that has a CR less than 1, but for humanoids you keep your equipment and not acquire the form's regular equipment, while Form of Artifice allows for turning into constructs or inanimate objects, but requires completing a long rest before using again.

Some traits relate to spellcasting as well, though don't give nearly as much power as a spell caster would. Morphed Spells can be acquired at character level 18 or higher, and allows for using spells and preforming the somatic and verbal components of spells in alternate shapes like the Druid class gets at the same level. It seems to be most useful if a few levels of the Morph class is taken at a high level with the character having a majority of their levels in a primary spellcasting class. Characters with only Morph levels and some spellcasting feats may be able to benefit, though not as much since the Morph class is not inherently a spellcasting class.

The amount of shapeshifting uses you get increases to three at level 8, four at level 15, and unlimited at level 20. You get to turn into forms up to CR 1/2 at level one and up to CR 9 at level 20 with the class. At third level you get the ability to speak normally in shapeshifter forms and also modify the appearance of your forms to have some superficial aspects of yourself.