you make 2 methods with the same name, one with progressbar, the other with webprogressbar (or nothing) as parameter
then in the second page of the inspector, you uncheck web or desktop to compile only for the needed paltform.
make two methods with different signatures (you can then set the Insepector/Gear Icon/Attributes/Include In flags to choose only Web or Desktop for each method)
one method that uses Variants, then internally switches on type:
MigrateAllUsers(iSAction as String, ProgV as Variant = nil, lblV as Variant = nil)
#if TargetWeb
dim prog as WebProgressBar = progV
#else
dim prog as ProgressBar = progV
#end if
prog.value = 32
[...]