Suggestion. Go "Preferences"Go Preferences and see "Keymap"Keymap.
"3D View"3D View > 3D View (Global) > View Navigation (Walk/Fly)
set to -> "3D ViewMouse (Global)", -> "View NavigationMiddle Mouse (Walk/Fly)" set to "Mouse" | "Middle Mouse" | "Press", Press (or "Click Drag") then "3D View" -> "View3D Walk Modal" -> "Confirm" set to "Mouse" | "Middle Mouse" | "Release"Click Drag)
Worked version 2.91.then
3D View > View3D Walk Modal > Confirm
set to Mouse , Middle Mouse , Release