Thanks for pointing that out. Does the lack of offload mean I would see more cpu usage then? I bought the cards in 2018 excactly because they were cheap as you say.
It *could* mean more CPU usage, yes. On the other hand, not all chipsets that have offload available actually have driver support for it, so it's entirely possible that it doesn't matter.
Without a description of your NAS, it's also entirely possible that you won't reach 10Gbps speeds even with the best ethernet chipset. For the obvious example, a system with a single 6Gbps SATA drive (~250MBytes/sec, ~2Gbps) clearly cannot fill a 10Gbps pipe on its own, and even a 100 drive array may have problems doing so if there's a lot of seeking involved.