Is this a weed or something I planted?

It isn't achemilla mollis. I know that one only too well. This is darker.
Could be geum but the leaves are a bit thicker and shiny. The tiny root threads . I think they were buried.

Anyway I've now planted it next to a plant which I don't know the name of either but it spreads. I've looked it up and it's :
Polygonum campanulatum or lesser knotweed. Anyone want some?

The stems of your plant have little climbing suckers. So maybe some kind of wall plant?

I downloaded an app to identify a plant that I wasn’t sure of.
I photographed the leaves and was informed it was a dianthus.
I still don’t know what it is but I do know what it’s not!
I deleted the app.
You could try it though. Hope you have better luck than me.

https://signal-corridor.live/uploads/talk/201903/medium-690649-alchemilla.png%3C/span%3E https://signal-corridor.live/uploads/talk/201903/medium-427764-alchemilla2.png%3C/span%3E

Could it be Alchemilla Mollis (ladies mantle)? This is some coming through in one of my pots although the leaf stalks are shorter.

I agree with SpringyChicken , some sort of Lavatera.

Wood aven. I must have had 'weed' in mind when I typed that/

The little yellow flower looks a bit like a weed aven, a wild form of geum, though the leaves aren't quite the same. If it was an aven, it would be a weed.

I'd pot it up and see what happens, what have you got to loose.

Lavatera rings a bell. I think the leaves are a bit sturdy for geum.
I'll plant it and see. Thanks ?

It looks like a geum to me. They tend to get a bit straggly over winter. Do you remember planting anything like this Grammaretto?

It's not a weed whatever it is. Wait and see when/if it flowers then you may be able to guess what it is.

Could it be a mallow (lavatera)?

Looks interesting. Put it in a pot and see what flowers!

Strawberry leaves? Hardy geranium?