Java Edition:Long Duration Blindness Effect
The blindness effect can currently only be obtained in survival by drinking suspicious stew, which can give a maximum duration of 8 seconds until 24w45a and 11 seconds since 24w46a. However there are methods in past versions that give blindness for a longer period of time.
Obtaining
Super Hostile Mode
In the red and purple versions of 2.0, the "Super Hostile Mode" event will take place. Aside from lightning strikes and many mobs spawning, the player will be given the blindness effect. The blindness will have a random duration between 15 and 30 seconds.
Illusioner
If the regional difficulty is above 2 illusioners have a chance to attack the player using a blindness spell, this will result in 20 seconds of blindness being applied to the player. Illusioners can be obtained in 20w14∞, 23w13a_or_b or 25w14craftmine, but once the illusioner is obtained, the long duration blindness effect can be obtained even outside these versions.