for the Timeless Child. It is a solid plot development that was executed well and has great potential. I have seen every surviving episode of Doctor Who, many of them multiple times, and the retcon (if that's even what the fuss is about) is absolutely negligible. Not a single line of the series needs to be rewritten to accommodate it. There have been far more impactful retcons in the past, where a new plot point directly contradicts previous canon.
This is not the case with the Timeless Child. We've already seen Time Lords regenerate into children, so nothing from the Doctor's childhood needs to be adjusted. One could say it retcons the whole Time Lord / 12 regenerations thing, but it does so in an interesting and logically sound way.
And think about it: the Doctor has always been unique among Time Lords. He has been praised and sought many times by Time Lords for his unique abilities. He alone was targeted by the Black Guardian, and we still don't know why. He alone saw the only way to end the Time War, and he alone survived.
So after several thousand years of being the most unique Time Lord in history, we finally find out why.
What's the problem?