Monstera tolerates a wide range of light and watering, but in both the wrong direction is the same one: too little light and too much water. Leaves without splits are not a disease, they are a measure of light, and yellow leaves are usually not thirst but the opposite.
Likely cause
Overwatering. Once the roots cannot get air they stop taking up water, and the plant looks like it is thirsty.
Don't confuse it with
It looks almost identical to underwatering. What separates them is the soil, not the leaf: put a finger 3-4 cm in.
Likely cause
Not enough light. The splits are a measure of maturity and light: normal on a young plant, a sign of low light on an established one.
Likely cause
Low humidity, or salts building up from the water. Very common next to a radiator in winter.
Likely cause
Mealybugs. They start in the places you do not look, so by the time they are noticed they have usually spread.
Likely cause
Fungus gnats. The larvae live in permanently wet soil, so the real finding is not the fly, it is the watering.
Don't confuse it with
Killing the flies removes the symptom and leaves the cause: the same thing returns in a few weeks.
Likely cause
Root rot: where overwatering ends up. At this point the plant has to come out of the pot and the rotted roots have to go.
Answering one photo is the easy part. With Monstera, whether the advice worked only shows days later, which is why Farmagile comes back and asks.
The misleading part of overwatering is that doing the right thing produces nothing in the short term. The yellow leaf does not turn green again and the plant looks the same for days. Whether it worked shows in the next new leaf, and that is weeks away. This is the plant where asking 'did it get better' earns its keep.
No account needed. You see the answer first.
This page is general information, written without seeing your plant. There are deliberately no product names and no doses: both depend on the plant, the region and the season, and a guessed dose on something you eat cannot be taken back.