Hi @ericonline,
Could you please share a bit more about the collection (workSummary) that you mentioned within your app?
Do you want to sum hours within the duration column of the collection (workSummary) and format the result as "##:##"?
I have made a test on my side, if you want to sum an hours column in a Collection using Sum function and Text function, I afraid that there is no way to achieve your needs in PowerApps currently.
As an alternative solution, you could consider take a try to create two collections to store hours and minutes separately. I have made a test on my side, please take a try with the following workaround:

Set the OnVisible property of the screen to following formula:
ClearCollect(workSummary,{duration:"02:30"},{duration:"03:00"},{duration:"01:00"},{duration:"00:15"});
ForAll(
workSummary,
Collect(HoursCollection,First(Split(duration,":")));
Collect(MinutesCollection,Last(Split(duration,":")))
)
On your side, you should type the following formula:
ForAll(
workSummary,
Collect(HoursCollection,First(Split(duration,":")));
Collect(MinutesCollection,Last(Split(duration,":")))
)
Set the Text property of the Label control to following formula (On your side, set the Default property of the TextInput control to following😞
If(
Len(Text(RoundDown(Sum(60*Sum(HoursCollection,Result),Sum(MinutesCollection,Result))/60,0)))=1,
Concatenate(
"0",
Text(RoundDown(Sum(60*Sum(HoursCollection,Result),Sum(MinutesCollection,Result))/60,0)),
":",
Text(Mod(Sum(60*Sum(HoursCollection,Result),Sum(MinutesCollection,Result)),60))
),
Concatenate(
Text(RoundDown(Sum(60*Sum(HoursCollection,Result),Sum(MinutesCollection,Result))/60,0)),
":",
Text(Mod(Sum(60*Sum(HoursCollection,Result),Sum(MinutesCollection,Result)),60))
)
)
Best regards,
Kris