PowerApps : Best Practice - Challenges in using of Date / Time data
Power Apps Canvas User Interface performs calculations on date and time data so that it will display properly. When a date and time for a User Local column is added through an FE app, an offset will be added or subtracted from the data based on the submitting user’s time zone. This is because when the Canvas UI retrieves and displays a User Local field, it will process the current user’s offset of the value.
Whereas in case of sending data through API (oData API) Canvas Apps User Interface is not involved at all, an easy solution to handle this challenge is to use UTC calculation or offset value or format date time values when passing through function calls.
More details can be found here - Using OData APIs to submit user local date and time values