What is this please?

[SugarPlumpFairyCakes]

Is it a weed?

I don’t know, but do you have an iPhone? It has a nifty plant search on photos. Or you could pop the photo into Google Lens (in a Google browser) and see if it comes up with any matches.

It looks like Greater Celandine.

lunatilly, you beat me to it by one minute

yes OP it is, greater celandine, which is invasive, but if you want plant cover its excellent,
as in, it is only a weed if you do not want it in your garden