Hello,
I'm using lookup function to update my A2 and A4 fields.
When entered value in A1, A2 gets auto populate.
When entered value in A3, A4 gets auto populate.
For A1 - OnChange below formula is added:
UpdateContext({var_employee: LookUp(SPListName,Title=Self.Text,ColumnName)})
For A2 - for Default below formula is added:
Coalesce(var_employee, Parent.Default)
But after submitting the form, A2 and A4 fields does not gets updated in form and SharePoint. It returns blank for both the fields.

Note: for lookup in A3 and A4, I've created a list to SharePoint.