Indirect and direct measurements of Hubble's constant show two very different values of Hubble's constant. Indirect measurements use the CMB, and hence are a reflection of the early universe's value of Hubble's constant. Meanwhile direct measurements use distance ladder techniques and are hence a reflection of the recent universe's value of Hubble's constant.

The two values disagree, over a range of experiments. The obvious solution is that Hubble's "constant" isn't really a constant and changes with time. However, this isn't anything new and it's well-known that H0 changes with time.

Why don't cosmologists just come up with a new model for how H0 changes at a different rate? This would fix the Hubble tension. How fucking hard can it be?