There’s hundreds of YouTube videos about this. You understand the exposure triangle? In this case you are looking at slowing the shutter speed without altering the overall exposure. So decrease shutter speed, increase aperture by the same amount of stops. If it’s bright and you can’t get the shutter speed down anymore (ie lowest iso and smallest aperture) then you’ll need a neutral density filter which effectively blocks out the light. You’ll need to manual focus (possibly before attaching the ND filter) and of course a tripod is pretty well essential.
Depth of field is a factor of the aperture selected, and nothing else. But to make the subject appear the same size when using crop factor lenses the subject needs to be further away from the camera. DOF increases with subject to camera distance (focal length) so cropped bodies / sensors appear to impact DOF because they are shooting at a longer focal length to achieve the same look. That’s one reason why cropped systems struggle to get as good bokeh / subject separation as full frame systems.
There are other factors regarding sharpness that could be at play. Most lenses have a sweet spot for sharpness at a particular f-stop (or focal length if it’s a zoom lens), which is not usually wide open.