Performing subtraction in SQL/finding the balance

SQL table here: http://sqlfiddle.com/#!9/abe1da/9

Current Table:

Year	Month	Type	Accounts	Amount
2021	1	Actual	abc	20
2021	1	Actual	def	30
2021	1	Actual	ghi	40
2021	1	Actual	X	7
2021	1	Actual	Y	3
2021	1	Actual	final	105

Expected

Year	Month	Type	Accounts	Amount
2021	1	Actual	abc	20
2021	1	Actual	def	30
2021	1	Actual	ghi	40
2021	1	Actual	X	7
2021	1	Actual	Y	3
2021	1	Actual	final	105
2021	1	Actual	BALANCE	5

SQL Attempt

select year, month, type,
case when accounts in ('abc') then 'abc'
 when accounts in ('def') then 'def'
 when accounts in ('ghi') then 'ghi'
 when accounts in ('X') then 'x'
 when accounts in ('Y') then 'Y'
 when accounts in ('final') then 'final'
else 'balance'
end as account_2
,
sum
(
(case when accounts in ('abc','def','ghi','final','x','y') then amount
else 
(
(case when accounts in ('final') then (amount))-
(case when accounts in ('abc','def','ghi','x','y') then -amount else 0))
)
from new

Note: That balance of 5 represents thousands of small accounts which currently do not form part of a database.

Answer

If I understand correctly:

select Year, Month, Type, Accounts, Amount
from new
union all
select year, month, type, 'balance',
       (sum(case when accounts = 'final' then amount else 0 end) -
        sum(case when accounts <> 'final' then amount else 0 end) 
       )
from new
group by year, month, type;

Here is a db<>fiddle.