Of top tier/high prestige competition, including both club and international football, which tournament has the fairest refereeing throughout the years? The UCL? World Cup? Euros? One of the top domestic European leagues? Factors include quality of referees and decisions, good VAR usage, least corruption etc.
CL is pretty good. Nations League is good. Bundesliga has a shout.
The WC is like a metronome. Swings from very good to very bad. Sometimes great, because the refereeing itself is good and uses tech well. But it also has a pretty deep history of corruption.