Just an idea I had: Make the Doctor forget all of their past lives.
They remember who they are to themselves, their values and their history on Gallifrey— but everything else, everything from William Hartnell to Ncuti Gatwa, is now gone from their mind.
The next time they meet The Daleks or the Cybermen or UNIT or Torchwood or anything will be, to the Doctor, for the first time.
A few benefits to this, as I see them:
It would remove the baggage from the character of The Doctor. Their personal history has started to loom too large in my opinion, and I think this would allow us to retain that history without it informing what’s happening on screen. The Doctor would be aware that there’s this legendary figure called The Doctor that they apparently are, but would have no memory of that.
It would allow The Doctor (and the audience) to have a sense of discovery again.
The show can maintain its continuity without being bound by it. If something that previously appeared shows up, audiences who know can recognise it and be excited, but if an audience member isn’t aware it will function as a new discovery.
Crucially— don’t make this a short term plot. I think they should not regain their memories for as long as possible, and maybe they should never regain it.