For Southern slaveholders, (broadly speaking) any sort of resistance from a slave was a serious offense, and was tantamount to inciting an insurrection. Keeping in mind that slaves were under constant supervision even during the war. This doesn't mean that there was no resistance, just that the consequences for getting caught were pretty severe. This doesn't mean that there was no resistance, just that it seems to have been mostly passive and not active acts of sabotage. Interestingly, this seems to have fed into southern racial stereotypes about slaves being lazy/stupid/etc. If a slave dragged their feet on, say, building a woodshed or intentionally washed the delicates in hot water and ruined them, or pretended to not understand their "owners" orders correctly, or loaded "masters" musket backwards, these are (likely) passive acts of resistence and would likely be dismissed by the overseers or owners without serious punishment.

When Sherman wrote about slaves being forced to fell trees into southern waterways to stop the US Navy, he mentions that they were accompanied by a good number of Confederate troops which were armed and more than ready to shoot. The consequences for what they broadly called "inciting insurrection" were famously severe and arbitrary, and the importance of keeping slaves in "their place" in a strict heirarchy was paramount to preventing the general slave rebellion that terrified slaveholders.

Slaves did seem to exercise a surprising level of political autonomy in resisting Confederate impressments to work by threatening their masters with running away if they were sent close to Union lines, as well as those smaller acts of defiance. It's unclear if this or selfishness was the ultimate reason that only a fraction of the requested slaves were ever provided to the Confederate war effort by the slaveowners it was protecting. However, it's important to note that at the time of the Civil War, being slaves was all these poor people knew-- they were born into it, their children were born into it, they were told their very religion not only condoned it, but demanded it. The people enslaved in WW2 were likewise considered "less than," but at the very least weren't immersed in being enslaved since before they were born-- and had (likely) at one point in time been given some sense of individual autonomy and self worth, as opposed to the people that were born considered property.

[I'm putting this as a side note, as I cannot remember which source this is from: It seems that the Confederate cavalry spent about 1/3 of its time on slave patrol, rotating between that and time with the campaigning Armies. The 20 slave law which exempted slaveholders from military service was largely intended to ensure that an appropriate amount of supervision was always at hand to keep slaves in check and constantly under the supervision of armed whites.]