You're trying to use the syntax for Calculate Field with the Calculate Fields tool. The syntax for Calculate Fields is:
arcpy.CalculateFields_management(in_table, expression_type, fields, {code_block}, ...)
#Or
arcpy.management.CalculateFields(in_table, expression_type, fields, {code_block}, ...)
The syntax for Calculate Field is:
arcpy.management.CalculateField(in_table, field, expression, {expression_type}, {code_block}, etc...)
#Or
arcpy.CalculateField_management(in_table, field, expression, {expression_type}, {code_block}, etc...)
As you're only calculating a single field, just change to using the Calculate Field tool:
arcpy.CalculateField_management(out_fc, tagid, value, "PYTHON3")
#Or
arcpy.management.CalculateField(out_fc, tagid, value, "PYTHON3")