̶E̶x̶e̶c̶u̶t̶e̶ ̶a̶t̶ ̶@̶a̶[̶g̶a̶m̶e̶m̶o̶d̶e̶=̶[̶g̶a̶m̶e̶m̶o̶d̶e̶.̶n̶a̶m̶e̶.̶h̶e̶r̶e̶]̶]̶ ̶d̶o̶n̶'̶t̶ ̶w̶o̶r̶k̶ ̶i̶n̶ ̶c̶o̶m̶m̶a̶n̶d̶ ̶b̶l̶o̶c̶k̶

/execute at @a[gamemode=!adventure] as @s run gamemode adventure 

/execute at @a[gamemode=creative] as @s run gamemode adventure