Add the ability to copy and paste into the expression box.
Currently the only way to enter an expression is to manually type it and hope you don't make any typos. Copy and pasting the expression would be much easier and quicker, and then appended an attribute.
The expression builder in general is difficult to work with. This would help a lot by allowing you to compose your expressions outside of the expression builder.
Similar idea from 2021, please add copy and paste to experience builder.
Option to Copy/Paste strings to Build Expressions ... - Esri Community