How to crop only one of nine layer with out adjusting the canvas size?

Hi

Sorry cant find the answer online. Photoshop 2023 (MacBook)
My PSD file has nine layers. Each layer is transparernt with one little object on it. Each layer is full canvas size, so there is alot of 'nothing' on each layer. Therefore the layer preview thumbnails all look the same>

So i want to crop each layer right down to the little object on that layer. But when i crop a layer, it changes the canvas to the size of the crop. I dont want to change the canvas. I just wnt to get rid of the dead space in each layer so that i can actually see the objects in the layer thumbnails.

I realise that might sound confusing. 

Even if i marquee around part of a layer, then cut and paste it back in to a new layer, the layer thumbnail hasnt zoomed into that area i marquee'd. 

Am i going nuts?

Thanks for any help
Simon