Comparing two lists is the core of reconciliation work: bank against ledger, last month against this month, ordered against received. Here are the simple ways to do it.
Method 1: COUNTIF
List 1 in A2:A200 and list 2 in C2:C200. In B2:
=IF(COUNTIF($C$2:$C$200, A2)>0, "In both", "Only in list 1")
Copy down. Do the same from the other side to find what is only in list 2.
Method 2: XLOOKUP
=XLOOKUP(A2, $C$2:$C$200, $C$2:$C$200, "Missing")
It returns the item if found, or Missing. The same formula can return a value from another column, such as the amount, to compare both.
Method 3: Highlight with conditional formatting
Select list 1, then Conditional Formatting, New Rule, Use a formula, and enter =COUNTIF($C$2:$C$200, A2)=0. Items missing from list 2 turn coloured.
Method 4: Unique and Filter (Microsoft 365)
=FILTER(A2:A200, COUNTIF(C2:C200, A2:A200)=0) lists everything in list 1 that is not in list 2, in one formula.
Clean the data first
Most false differences come from extra spaces, upper and lower case in codes, or numbers stored as text. Run TRIM on both lists before you compare.
Compare amounts, not only names
After matching IDs, subtract the amounts: =C2-D2. Anything not zero is a difference to investigate.