my roto brush tool works, but when i want to remove unwanted areas by holding alt, its not working.

[Dishika34849530yh9d]

the red circle is not showing. what can i do

[Thaumar]

This is probably not it, but there are regularly Wacom driver issues where modifier keys with the Wacom pen are not working/being ignored. If you are using a Wacom tablet, updating (or going back to an older version) the Wacom drive might solve it. Just a long shot...