Forge 1.21.1, the latest version of the mod for this version. Even if I enabled the breaking option in the config, they still don't break any block

Are you talking about vanilla zombies or my horde zombies?

Both, I surrounded myself with dirt blocks and they can't break them

only horde zombies should work in the current release (vanilla zombies will come in the next release).
can please post your main config?
were they spawned in by a horde?

Yes, I used the CountdownMessage to make sure it was a real horde. I also tried waiting for another horde, but nothing, they still don't break any blocks.

My config:
#If true, Nights of the Undead (horde nights) are enabled | default: true
undeadNightsEnabled = true
#Days between horde nights (1 = every night is a horde night) | default: 5
#Range: > 1
daysBetweenHordeNights = 1
#Chance in % for a horde night | default: 100
#Range: 1 ~ 100
chanceForHordeNight = 100
#If true, each night a message will be sent to the player with how many nights are left before the next Horde Night | default: false
sendHordeNightsCountdownMessage = true
#Minimum distance a horde will spawn away from the player | default: 70
#Range: 10 ~ 256
distanceMin = 70
#Maximum distance a horde will spawn away from the player | default: 75
#Range: 10 ~ 256
distanceMax = 75
#Maximum amount of horde mobs that can be loaded in the world at the same time | default: 80
#Range: 1 ~ 2048
hordeMobsSpawnCap = 80
#If true, additional waves can spawn in a horde night | default: true
spawnAdditionalWaves = true
#Time in seconds between check for next possible wave in a horde night | default: 45
#Range: > 1
cooldownBetweenWaves = 45
#Chance in % for another zombie wave (checked after every wave cooldown) | default: 7
#Range: 1 ~ 100
chanceForAdditionalWaves = 100
#If true, horde waves can spawn in water | default: false
hordeWavesCanSpawnInWater = false
#If true, horde waves can spawn on trees | default: false
hordeWavesCanSpawnOnTrees = false
#If true, Players can't sleep through horde nights | default: true
hordeNightsDisableSleeping = true
#If true, the horde zombies will be persistent and not despawn | default: false
persistentMobs = false
#If true, the horde zombies (only those added by this mod) will burn in daylight | default: false
hordeZombiesBurnInDaylight = false
#If true, Horde Zombies can break blocks | default: false
hordeZombiesCanBreakBlocks = true
#Horde Zombie block break tier (0-3) | default: 1
#Range: 0 ~ 3
hordeZombieBlockBreakTier = 3
#If true, single stray horde zombies can spawn on normal nights | default: true
spawnStrayHordeZombies = true
#If true, debug messages will be logged out | default: false
printDebugMessages = false

hm... I'm still not able to reproduce this, what other mods do you have installed?

Could you please turn
#If true, debug messages will be logged out | default: false
printDebugMessages = false
to true?

Ok, problem solved. I removed all the other AI mobs mods, and now it works, thank you

no problem
out of curiosity do you know what mod caused the issue?

I'm not sure which one could've caused that. Maybe with the "improved mobs"