Capablanca-Tartakower

New York 1924 rd6

White to play

This is a well-known classical endgame where the 35.Kg3! was played

After 36..a6(Diagram)

preparing ..b5 with queenside counterplay is deeply analyzed by Müller in Understanding Rook Endings(Gambit 2016)

After 36..a6

36..Rf3 was the game continuation

After 38..bxa4(Diagram)

It looks like the a-pawn will give some counterplay

What do you recommend for White?

After 38..ba