Use “%%” in like condition:
select
it.item_group as "Item Group",
max(cast(mid(it.item_code,5,6) as unsigned)) as "Reference",
concat(mid(it.item_group,1,4),lpad(cast(max(cast(mid(it.item_code,5,6) as unsigned)) as char),6,'0')) as "Latest Item Code"
from tabItem it
where it.item_group not like 'T%%'
group by it.item_group