I’m assuming though that whilst footpaths (green dashed) are public rights of way and access to them is legally enforceable, paths (black dashed) don’t enjoy that right? Or does the fact that they appear on an OS map make a difference as opposed to being on Open Street map for instance?
Yes you have a legal right to walk on a green dashed path as it is a PROW. A black dashed path on an OS map just means that there is (at one time anyway) a physical path on the ground. This does not imply any right of way in England and Wales.
Paths shown on OSM and not tagged as being PROWs also do not imply any right of access in England and Wales either.
Both depend on whether the path is in Open Access land or if on private land whether the landowner has given permission for its use by the public, if so, you have a right to walk along it subject to any conditions e.g. on grouse moors etc. Permissive paths are sometimes closed for one day per year by the landowner to prevent it becoming a PROW and you would have no right to walk along it on that day.
In Scotland of course you have the right to roam along any paths shown on OS or OSM providing you do so in accordance with the Scottish Outdoor Access Code.The sooner England and Wales adopt the Scottish model of access the better.