Combine my advice with the above advice. Use a monster red 18mm on a silt hook 4 IQ-D rig. You want to fish all of the catfish into an cove, this will prevent them from outrunning your line. You’ll need to make a point of finding where you catch them and where they surface. Catfish have an unusual way of rendering themselves on top of the water, pay attention, and then throw your rigs where they’re patrolling.
Ignore other baits when going for catfish and only use the 18mm red monster. If you don’t have lac le dor map use the Spanish lake instead and use the same rig set up, you’ll be mostly ignoring regular carp in my approach which is the advantage over using other baits and strategies. Again, find their paths and lure them through these.
In my experience they appear the patrol the outer rim of the water about 2-6 feet from the shore, so don’t be afraid to cast a few feet in front of you, you’ll catch more basic carp this way, but if you see them surfacing don’t be afraid to throw your hook in. If you can find their patrol more than 60 yds away this is where you’ll get most of your cats and this will ignore most carp around 30lbs or less. This is the advantage of this strategy.
Another good piece of advice is to ignore all hook nears the red monster, in my experience those hooks appear the be nicer but in reality they’re not. Stick to the more basic haichou rigs with the white plastic weed guards, any other hooks will slow down your progression through the game.