simple:
declare @d varchar(20) = '2024040611102200021'
select cast(SUBSTRING(@d,1,4) + '-' + SUBSTRING(@d,5,2) + '-' + SUBSTRING(@d,7,2)
+ 'T'
+ SUBSTRING(@d, 9,2) + ':' + SUBSTRING(@d, 11,2) + ':' + SUBSTRING(@d, 13,2)
as datetime)