create table T (dt datetime, t float);
insert into T values
('2022-05-15 09:00:00', 18.36),
('2022-05-15 11:00:00', 21.6),
('2022-05-15 18:00:00', 17.8),
('2022-05-16 09:00:00', 17.3),
('2022-05-16 11:15:00', 18.36),
('2022-05-16 19:45:00', 20.62);
select FORMAT(dt, 'yyyy-MM-dd') as d, max(t) as t
from T
group by FORMAT(dt, 'yyyy-MM-dd');