Flow Action - Auto populate date when certain value selected in choice field

[RichardEagles]

Hi all,

Is it possible to use a flow to auto populate a date field when you select a certain value from a choice field?  I've read that using a calculation field is not the best way as it'll update whenever the record is updated, however in this case, the completion date should always remain the same.

Many thanks.

[#2]

On edit or update trigger , than switch and set date and time from variable.