My implementation of a “universal remote” in Home Assistant, was simply to use a picture of a Harmony Classic Remote device, and assign actions to each button:
The YAML code associated with this card is too long to paste here, but you’ll find on Pastebin; Harmony Remote YAML - Pastebin.com
In addition, it require a script.yaml that takes care of adapting the key presses dependingon the chosen activity at any time (TV, Radio, Media Libray, Apple TV, etc.). This script is also on Pastebin: Media selector Script - Pastebin.com
Note: I have expanded the code somewhat since this early version, but the principle is the same throughout once you understand how it works.
I have had this for several years now, and never ever had any issues with it. It also works fairly well on a Mobile phone screen - even though the buttons are a bit too small.
Nobody in my household ever bother to look for the remote control anymore. They’ve all got their own copy 