When the difficulty is set to peaceful, trial spawners will never try to spawn mobs and will get stuck in the waiting_for_players state. This occurs even with passive mobs such as a pig, which is inconsistent with regular monster spawners.

There was a similar bug report about this MC-266556, however this wasn't properly fixed as now the trial spawner gets stuck in the waiting_for_players state and won't actually try to spawn mobs, instead of staying inactive

Steps to reproduce:

1. Set the difficulty to peaceful
2. Place a trial spawner in a grassy area
3. Right-click on the trial spawner with a pig spawn egg
4. Go into survival mode
5. Look at the trial spawner with the F3 screen enabled
6. Notice how the trial_spawner_state never changes from waiting_for_players

Expected result:

The trial spawner should go into the active state and spawn mobs which are passive.

Code analysis:

In net.minecraft.world.level.block.entity.trialspawner.TrialSpawnerState#tickAndGetNext, when the state is WAITING_FOR_PLAYERS the TrialSpawner#canSpawnInLevel method is called.

case 1 -> {
        if (!trialSpawner.canSpawnInLevel(serverLevel)) {
            trialSpawnerData.resetStatistics();
            yield this;
        }
        if (!trialSpawnerData.hasMobToSpawn(trialSpawner, serverLevel.random)) {
            yield INACTIVE;
        }
        trialSpawnerData.tryDetectPlayers(serverLevel, blockPos, trialSpawner);
        if (trialSpawnerData.detectedPlayers.isEmpty()) {
            yield this;
        }
        yield ACTIVE;
    }

The canSpawnInLevel method in net.minecraft.world.level.block.entity.trialspawner.TrialSpawner always returns false on peaceful difficulty and doesn't check if the mob is passive, resulting in the spawner never trying to spawn passive mobs

public boolean canSpawnInLevel(ServerLevel serverLevel) {
    if (this.overridePeacefulAndMobSpawnRule) {
        return true;
    }
    if (serverLevel.getDifficulty() == Difficulty.PEACEFUL) {
        return false;
    }
    return serverLevel.getGameRules().getBoolean(GameRules.RULE_DOMOBSPAWNING);
}