Description
The append layer field type must match the type of the input layer field you want to append to.
Solution
This is a warning and should be expected if your layers have fields with the same name and different type, or if you have incorrectly mapped fields.
For example, the Append Fields parameter is correct when you map text fields to text fields, and double fields to double fields.
Use the Append Expressions parameter to alter field values with Arcade expressions.
Learn more about Append Data expressions
Create or calculate an append layer field to match the input layer field using the Calculate Field tool.