The Fifteenth Doctor is still finding his feet in Doctor Who, but the Christmas special helps to highlight what is still going wrong. With every regeneration, there is a transition period where the audience and the Doctor needs to find the Doctor within the new face. At times, this change can happen quickly, and the new Doctor can settle into his role as the time-traveling hero without missing a beat, but at other times, the show struggles to really land the Doctor with his new identity.

https://screenrant.com/doctor-who-fifteenth-ncuti-gatwa-season-15-problem-op-ed/