Am no expert but looks like a Coaltit with leucism
You can read more about the condition below
https://www.bto.org/our-science/projects/gbw/gardens-wildlife/garden-birds/behaviour/plumage/leucism
(Pardon the Scottish Accent)
Are you in Britain? just in case we need knowledge of overseas birds rather than looking at 'oddities'.
Cin J
Derbyshire, uk.