Note: I am using the semicolon ";" as the list separator because you probably have one. If you have an error, change the semicolon ";" to a comma ","
Code:
=IF(DATE(G2;F2;1)<DATE('TVöD Bund Jul 23 - Feb 24'!$K$1;'TVöD Bund Jul 23 - Feb 24'!$J$1;1);INDEX('TVöD Bund Jul 23 - Feb 24'!$B$3:$G$21;MATCH(B2;'TVöD Bund Jul 23 - Feb 24'!$A$3:$A$21;0);MATCH(C2;'TVöD Bund Jul 23 - Feb 24'!$B$2:$G$2;0));INDEX('TVöD Bund ab März 24'!$B$3:$G$21;MATCH(B2;'TVöD Bund ab März 24'!$A$3:$A$21;0);MATCH(C2;'TVöD Bund ab März 24'!$B$2:$G$2;0)))*D2