Things actually have gotten more and more closed, e.g. of stuff getting paywalled with time:
It appears that things got really bad starting in 2017, possibly when WebLearn was introduced. When things migrated to Canvas, they were closed by default, apparently with any mechanism to publish publicly.
Therefore, they managed to make things more closed than when teachers would just upload to good old
ox.ac.uk/~name static websites!!Ciro Santilli has also heard that some people in the Mathematical Institute of the University of Oxford opposed to moving away from their Moodle instance precisely because the new options did not support open publishing, so kudos to those people. But most teachers likely don't care and just do whatever is the best internally supported default.
Their "open" video material: podcasts.ox.ac.uk/ A somewhat small part is Creative Commons, but most proprietary. Despite the name "podcasts", they do contain video, it is just a relic.
podcasts.ox.ac.uk/open contains actual Creative Commons only it seems.
It does however appear that professors own their lecture notes, so there some hope maybe: governance.admin.ox.ac.uk/legislation/statute-xvi-property-contracts-and-trusts#collapse1383636
Talks: talks.ox.ac.uk/. Mathematical, Physical and Life Sciences (MPLS) subset: talks.ox.ac.uk/talks/department/id/oxpoints:23232639