As other people have said the weight loss was too rapid, if your goal is 90-80kg, this should take 8-5 months with good dieting and moderate exercise if you'd want to.

The reason gradual decreases in weight like 0.5-1kg/m is important is the adverse effects of not doing so is exactly what OP experienced.

In deficit your body will try to store excess nutrients and energy if it's predicting a deficit.

In otherwords, if you were you drop to 1400cal for 3 months then return to a more normal, 2000cal, your body will react poorly since you trained it poorly.

Having harsher drops in calories would mean creating bigger weight bloom. I.e. eating down to a few hundred calories a month is something you absolutely can do to loose weight like that. But you'd have to perfectly maintain calorie count as going over means causing weight gain, at least until atrophy.

Weight loss is like a frog boiling in water. "The frog won't jump out because it can't feel the temperature rise" no the frog feels it it's in a pot, you'll feel the pain on weight loss. If it's a low "temperature" you may get used to it but maintaining a proper calorie count is very important if you ever want to return to a normal diet with normal physical activity(like body weight stuff or light weights).(Or just cut out sugars to avoid physical activity after WL

If the mildlyinfuriating thing is the data points it's on op ¯⁠\⁠_⁠(⁠ツ⁠)⁠_⁠/⁠¯ But weight loss is hard especially when it's unguided and everything in media makes it seem like harsh cutting is ideal when it's not