Clay is good in some ways, as it holds food for plants better than a sandy soil.
The advice is to add as much organic material as you can, compost, manure etc.
Also do an acidity test. Depending on the results of that, add lime. Lime makes the fine flat particles of a clay soil bind together( flocculation) and improves drainage.
It takes a while to change a soil, but it can be done.

OB is dead right; clay soil will hold onto nutrients better than light soils and so won't be washed away. Light soil or sandy soil is often called 'hungry soil' as it needs the constant addition of feed and compost. I would be inclined to dig in, not only any old compost but buy in some bags of sharp sand. I would go for ordinary sharp sand although it contains some lime, isn't anywhere as expensive as horticultural sand. If you find a bit overwhelming, then treat the soil each time you plant something new.

Thank you very much both. I’m the meantime while it’s taking time to improve are there any annuals I could plant just to get colour ? And would clematis do ok ?

Clematis like an alkaline soil, which retains moisture, so yes. Dig in grit and compost when planting.
As long as the garden does not flood or has standing water, then most annuals would grow, except perhaps for the ones which prefer really sharp drainage, like Antirrhinums (Snapdragons).
Basically there is only one way to find out what will grow....plant and see.

Thank you ! I’ll definitely get a clematis and experiment with the annuals

I used to have clay soil in my previous garden, and Owdboggy’s advice is spot on. I would just add, add a good handful of grit with EVERYTHING you plant.

Just wanted to show you a photo of the clematis I’ve planted. It’s not in the ground at the moment I put it
in a pot in the end for now in case it’s too
much in the shade
It’s a Westerplatte and for now looks very healthy