Join tables on ID and put the difference into the where clause.
Sample data (you have it & you don't have to type that):
SQL> with
2 table1 (id, name, salary) as
3 (select 1, 'x', 500 from dual union all
4 select 2, 'y', 1000 from dual
5 ),
6 table2 (id, datum, salary) as
7 (select 1, date '2022-01-01', 500 from dual union all
8 select 1, date '2022-02-01', 300 from dual union all
9 select 1, date '2022-03-01', 500 from dual union all
10 select 1, date '2022-04-01', 700 from dual union all
11 select 2, date '2022-01-01', 1000 from dual union all
12 select 2, date '2022-02-01', 1000 from dual union all
13 select 2, date '2022-03-01', 900 from dual union all
14 select 2, date '2022-04-01', 1200 from dual
15 )
Query begins here:
16 select a.id,
17 a.name,
18 b.datum,
19 b.salary - a.salary as difference
20 from table1 a join table2 b on a.id = b.id
21 where b.salary - a.salary <> 0;
ID NAME DATUM DIFFERENCE
---------- ---- ---------- ----------
1 x 01.02.2022 -200
1 x 01.04.2022 200
2 y 01.03.2022 -100
2 y 01.04.2022 200
SQL>