On the website of the Grand Duchy of Luxembourg it is fascinating to read this statement about public transport...
"Public transport in Luxembourg is a quick, clean and free way of getting from A to B. Yes, you read it correctly, it’s “free”! Since 2020, all forms of public transport, including buses, trains and the brand-new tram, are free throughout the entire country. With a network that constantly adapts to the needs of its passengers and the addition of the tram, this mode of transport is becoming increasingly popular among residents and visitors alike".
More from the Luxembourg Government...
Since 29 February 2020, public transportations has been free for everybody, residents as well as tourists. This is the case for trains, trams and buses (RGTR, TICE, AVL). In other words, you don't need to buy a ticket anymore. The only exception are tickets and subscriptions for the 1st class, which still have to be paid for.
However, every passenger has to be able to show a piece of identity if a conductor demands to see one "