What type of soil do you have in that area and do you have an idea of how deep it is? If it’s in good condition and free draining you could consider a shade tolerant grass like Hakonechloa macra, an evergreen fern such as Polystichum setiferum or, if you want flowers, a hardy geranium (cranesbill, not the tender pelargonium).
Woodruff ( Galium Odoratum) is a spreading and matt forming perennial which likes shade. It has lovely little white flowers in summer. We have grown it near a pond, in the past, and it spread nicely around it. Any creeping bits that come up are easily pulled out so you could contain it to the area where you wanted it. We currently have some in a pot which is in the shadiest part of garden, facing ( slightly) North East.
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