Hi, It is working for me now, I updated the firmware of my Deco M4 to 1.5.0 through the static.tp-link.com url and then I could see the option to change service name in the Deco app once I selected...

@TP-Link any update on this please? Even I'm facing the same issue (using a Deco M4). Its March 2021, but no firmware update yet.