The alto sax can play transposed F6. There are some alto saxes with an extra key for f#6. If the default notes don't play, then change sound fonts. There are many like the General User GS with larger ranges than fluid (the default). see https://musescore.org/en/handbook-sound-and-playback/soundfonts#list
Comments
It should play up to C6/Eb6, everything before the notes turn red to mark them outside playable range, and does for me.
In reply to It should play up to C6/Eb6,… by Jojo-Schmitz
I thought Alto sax should play up to C6/F#6
In reply to I thought Alto sax should… by Maesro
The alto sax can play transposed F6. There are some alto saxes with an extra key for f#6. If the default notes don't play, then change sound fonts. There are many like the General User GS with larger ranges than fluid (the default). see https://musescore.org/en/handbook-sound-and-playback/soundfonts#list