I don't use this remote control (delivered to a friend).
There is a teletext button (button 13 on the manual)
https://www.oneforall.com/sites/default/files/2018-10/urc1910_manual_en_de_fr_es_pt_it_nl.pdf
Yes, this remote control is compatible with the UE40MU6170.
You can find more information on the manufacturer's page, as well as various setting codes if necessary: https://www.oneforall.de/ersatzfernbedienung-fur-alle-samsung-tvs.html
My TV is over 6 years old and I have had no problems. If it doesn't work right away, the remote control can "learn" the TV, which is described quite well in the instructions.
This sounds to me more like problems with the TV settings than with the remote control. With my Samsung TV, I was able to use this replacement remote directly as if I had never had another one.