You could use dowels, but I’d recommend using something to actually hold the tabletop to the legs, I’m not sure loose dowels by themselves going into slots (you wouldn’t want tight fitting dowels in more than one spot along the leg) would be enough. Dowels plus z clips or blocks would probably work; you could also route a shallow channel (5mm or so) in the bottom of the tabletop that the legs slot into (prevents sliding but wouldn’t constrict wood movement) and fix with z clips. Also instead of screwing the z clips in you can use threaded inserts and a bolt so you can retighten/take apart many times.
If you look towards the end of this post you can see how I did my coffee table: Coffee table
Or towards the end here how I’ve done our desks (they only clamp to the frame on the ends: Beech desktop for standing desk frame
Neither of these have had any problem with sliding/racking