Dry Wall Cavity Insulation

Is it worth it?

I own a new build bungalow, I've been doing some cabling work and whilst doing that noticed the dry wall cavity is open to the loft space all the way along the length of the (dry) wall top. The rafters behind each gable end only partially cover this cavity.

The loft stays very cold when the house is warm as there is a huge amount of loft insulation above the ceilings. It's double and even triple layered in places over the entire loft area, except for a narrow strip of loft boards for access.

It's satisfying that the roof tiles stay frosty all day when they don't get any sun on them but that's also making me think the dry walls must be drawing some warmth up into the loft space with the cavity behind them being open to the loft.

I don't know if this is normal in construction but was very glad it was open and accessible when fish taping the cables through into the loft space.

Now that the cabling is done it's occured to me it might be better if this dry wall cavity wasn't open at the top and that the cavity be sealed all the way along the top at the very least.

I've briefly looked around and one option that caught my attention was cork crumbs as an alternative to drilling holes and using expanding foam.

Just posting this here to hopefully get some opinion about whether it's wise/worth doing and what might be the best/most economical option if it is. TIA