Maybe it's better to keep the list column type (e.g. for sorting).
If so, convert your date string ('31/03/2023') to an ISO formatted date string (e.g. '2023-01-31').
This is accepted as a sharepoint date value.
Assuming that outputs('Compose') is your date string:
concat(outputs('Compose')
split(outputs('Compose'), '/')[2],
'-',
split(outputs('Compose'), '/')[1],
'-',
split(outputs('Compose'), '/')[0]
)