I have been AFK for over ten hours on superflat for one of those pillager patrols, but not one spawned, despite them spawning every hour at most on other world types.
To reproduce, create a superflat world, then run the command:
execute at @e[type=minecraft:pillager,limit=1] run playsound minecraft:block.note_block.bell voice @p ~ ~ ~ 1 1
This command will be used to make an alarm that alerts that you detected a pillager. The last step is to AFK until a pillager spawns and activate the alarm.
If you AFK in a non superflat world, a patrol should spawn in and activate the alarm in about 30 minutes, but if you AFK in superflat, they won't ever spawn, even if you wait for about half a real life day!
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Same! I think that is happening to everybody. In the next snapshot, they probably are going to increase to the spawn rate.

If you give yourself the bad omen enchament, does it still happen?
When I use the bad omen effect, a raid will happen but I won't be able to see any patrols (an illager gang lead by a leader with a banner on it's head). The only way to trigger a raid at all is to kill the leader of the patrol, which cannot spawn; therefore it is impossible to trigger a patrol or raid without commands.

Mojang did this intentionally: This is what they added under Illager Patrol page on the wiki under History: "Illager patrols now spawn in the world less often."
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I can at least confirm they still spawn but they're very rare and spawn alone.
I was now AFK in a normal minecraft world for under 2 hours and during the day, a patrol finally spawned! I guess these patrols are really just that rare, or maybe they don't ever spawn in superflats or buffet worlds. I might further analyze the spawning mechanics tomorrow to see whether or not they can spawn in superflats or buffet worlds. I may have been a bit late and I may have not had much information in the report, but I finally fixed it so now it can be confirmed.

Resolved as invalid for now until we hear back from you.
Please reopen, I have confirmed in 19w09a that patrols never spawn in superflat after waiting for over twenty minecraft days in one minecraft world. I have followed every step on this report and have not triggered any unnecessary controls that could have prevented patrol spawning (gamerules, peaceful difficulty, added light sources, wrong biome (I used Overworld preset without editing), or spectator mode). I have seen two wandering traders, which only spawn every 14 minecraft days on average before I saw the illager patrol that I have seen spawned multiple times in other worlds (when I was exploring in creative or survival mode). This shows that the problem still exists in 19w09a, and that it's now valid since I confirmed it again much later. (I may have also deleted the other comment that was in the same place as this one, but that was because it had information that was not needed due to this one having better information)
Also, I think the screenshot that cites the wiki is no longer necessary because it made a claim that they were supposed to be rare. That screenshot was attached before I confirmed that the spawning issue only happened on superflats (due to me testing this on a superflat at first), meaning that it is outdated. It should be removed because it no longer rebukes this ticket due to this being an actual problem as shown earlier in this comment.
Thanks for reopening, I will continue to update the affected versions (starting tomorrow assuming there will be a snapshot at that time assuming this will not be fixed by the next snapshot)

Still affects the 1.16 snapshots so far.. is this planning on being fixed?

I can confirm that Patrols does NOT spawn in superflat. I am a superflat inthusiast. I have a 1.15.2 server that is up for 267 minecraft days. My basement is in a village. I am exploring other villages, searching explicitely during the day and night for patrols. Till now (day 267) there was no single one patrol.
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One extra note - you cannot be within a few chunks of a village for a patrol to spawn. I tested in a superflat world and saw a patrol spawn given I was far enough away from the village. Can someone confirm this bug still exists when standing far enough away from a village?

Suggesting closure of issue- a popular YouTube video uploaded by user Luke TheNotable demonstrates the spawning of a pillager patrol in a superflat world in 1.16.
I went AFK for 2 hours in the "Redstone Ready" superflat world (which has absolutely no villages). Despite the fact that I had the doMobSpawning
and doPatrolSpawning
gamerules enabled, not one patrol spawned.

Can confirm in 1.20.4 and 24w07a, it's MUCH easier to reproduce this issue thanks to the addition of "/tick"

Pillager patrols spawn normally on 1.21 in my very old superflat world

I created new standard superflat world (
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