I found the solution, I can't use LookUp queries and other operations in the If function in the OnSave property. But I don't know what causes this problem, it doesn't happen when using a custom form in a List, but it doesn't work in a Share point page.
Not available on Share point pages.
If(LookUp(
[@DataSource],
Title = DataCardValue1.Text,
Status
).Value = "xxx",Flow())
OK:
If(DataCardValue1.Text = "xxx",Flow())
Is it possible to assume that the query function cannot be used in the If condition of OnSave.