Pillager Patrolling AI does not and has not worked for 2 years now. It has been this way ever since December 2019 when 1.15 came out (the update that broke it)
You can try it out for yourself:
/summon minecraft:pillager ~ ~ ~ {Patrolling:1b,PatrolLeader:1b,PatrolTarget:{X:60,Y:60,Z:60}}
When the Pillager spawns, it will set their NBT data accordingly, but it will instantly unset the "Patrolling" NBT tag from 1b to 0b.
Changing this data manually with /data merge entity @e[type=minecraft:pillager,sort=nearest,limit=1] {Patrolling:1b} will not fix it, it will instantly default back to 0b, unless you are not in creative mode and are within aggro range of the pillager.
Even if they happen to keep their Patrolling NBT data at 1b, they will not path to their PatrolTarget location.
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We're tracking this issue in MC-236846, so this ticket is being resolved and linked as a duplicate.
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