A formula such as =IF(AF30="Stopped",G30,VLOOKUP($AD30,Data_D!$A$6:$G$2256,6,FALSE)) is a "standard" formula, there is no need to confirm it with Ctrl+Shift+Enter.
The formula =MAX(IF(B5:B30<0,B5:B30)) is an array formula because the first argument of IF is normally a single condition, but here there is a condition for each of the cells in B5:B30. Hence, IF(B5:B30<0,B5:B30) does not return a single value, but an array of values. Such formulas must be confirmed with Ctrl+Shift+Enter.