Retirement tax questions

There are many different MAGI for different things.  That must be the worksheet for Form 8582, it's between p1 and 8582 p2.  It should say at the top which form it applies to.  

Also it is too late to affect your 2026 SS IRMAA.  Have you got your SS letter yet?  I got mine at the beginning of December.  It uses your 2024 AGI plus line 2a.  Here's mine for 2026, it has the brackets listed.