If you use a swivel do not attach it directly to the anchor. Attach a few links of chain, then the swivel and finally the main chain. This means that the swivel always pulls in a straight line.
I have abandoned using a swivel. When removing mine to turn the chain, the hex bolt that holds it together had suffered serious metal deterioration and disintegrated. None of this was visible, and I was lucky not to have lost the anchor. I have not had any serious chain twisting issues even in strong tidal streams.
It was a Kong Swivel which I refastened every time I turned the chain end to end ( at least biannually).
Ian ‘Ocean Hobo’
Isles of Scilly