Adding percent symbol to a dynamic measure

[RingoSun]

QtyOrPercent = 
VAR Selection = SELECTEDVALUE('View Options'[Options])
RETURN
SWITCH(
    TRUE(),
    Selection = "By Percentage", [QTY %],
    Selection = "By Quantity", [QTY]
)

I have this measure above and basically I am switching to either percentage or just the plain sum based on the selected option on the slicer. My issue is I want to add a percentage symbol if the percentage option is selected. Using the Formatting option isn't viable here as it would turn the plain Quantity value into a percentage as well. 

What are my options here? I tried doing something like below but it didn't work and my line graph became empty.

QtyOrPercent = 
VAR Selection = SELECTEDVALUE('View Options'[Options])
RETURN
SWITCH(
    TRUE(),
    Selection = "By Percentage", FORMAT([QTY %], "Percent"),
    Selection = "By Quantity", [QTY]
)

[amitchandak]

@RingoSun , I think you should consider the field parameter for this release in May 2022, or the calculation group

Discussed both in Blog and video at the end of blog - https://medium.com/@amitchandak/power-bi-field-parameters-a-quick-way-for-dynamic-visuals-fc4095ae9a...