The answer is wholly dependent on the level of competition. Beginners tournaments result in many more and completely different arbiter "interventions" than norm tournaments, for example. They have also changed over time as players get to know what is and isn't allowed and adjust their behaviour accordingly.
For instance, in the early 2010's far too many of my interventions involved players who had forgotten to switch their phones off. That never happens nowadays in my tournaments.
I would say that the one type of infraction which happens across all levels of tournament is spectators with switched on mobile devices (both phones and tablets). These are normally relatives, usually parents, of competitors who probably just want to "keep in touch" with the outside world via social media. Very occasionally they are chess-knowledgeable friends of one of the competitors who have to ask mobile Fritz what he thinks of their friend's position.
The devices have to be switched off and put away else their owners will be ejected from the playing area. An exception can maybe be made in blitz tournaments where players don't have time to leave their seats.
Beginners
Illegal move is the number one particularly for young players. Towards the end of a round with young, inexperienced players you spend all your time responding to a sea of raised hands and a chorus of "Illegal move!". You also get the occasional "touch move" but young players are pretty good with this.
Weak/Old players
Both weak players and older players seem to have a problem writing the moves down. Some weak players when it's clear to them that they are going to lose feel it is OK to play on, not resign, but stop recording the moves. I've never actually defaulted somebody in that situation for not writing the moves but I've been tempted when the same player does it more than once.
Older players sometimes "forget" that when they have a 30 second increment they have to continue recording even when they have less than 5 minutes on the clock. Older players can also be cantankerous about this. Strangely I've see it extend as high up the scale as 2200 rating.
Strong/Master Players (2200+)
The only tournaments where there is much in the need of arbiter intervention are blitz tournaments where when the players get down to the last few seconds then illegal moves are more likely. The players are generally very knowledgeable and don't break the rules. I get the very occasional draw claim but usually players agree a draw when they start repeating or not making any progress while getting closer to the 50 move rule and they don't need my "help".
In longer form tournaments it's probably post-game analysis which is the main problem. It doesn't happen all that often at an obtrusive level. If the players are whispering quietly and not disturbing the other players I usually let it continue for a minute or two before intervening. At this level the players are quite clever. They are perfectly capable of placing the kings appropriately in the center (required for DGT live board broadcasting) all the while continuing their analysis without moving the other pieces. If they started moving pieces before placing kings I would get quite cross, not because they'd broken any rules, but because they disrupted the live broadcast.
The only time I've ever leapt in is when one or more players from other active boards have felt the need to join in at the end of a particularly exciting game. They were "analysing a game on another board" which is forbidden, even if it had nothing to do with their own game. It is also usually much more disturbing for other players.
