BBC Four began originally as a late schedule to BBC Two aka BBC Knowledge so that’s where the OU connection comes in.
Though BBC Four shows a lot of old programmes, it is (or was) required by its licence to air at least 100 hours of new arts and music programmes, 110 hours of new factual programmes and to premiere 20 foreign films each year. My understanding is that it’s the original programming which will be lost. The Guardian reported on 29 March 2021:
BBC Four is to cease commissioning new programmes and become an archive-focused channel as part of the ongoing significant cost-cutting drive across the corporation.
It also says:
While the corporation announced plans last week to double its arts and music spending on BBC Two, it annual plan stated that “this approach will necessitate a shift away from commissioning a high volume of lower-cost programmes on BBC Four, which are less effective at reaching audiences on the channel and on iPlayer”.
That’s a matter of opinion. BBC Four gave us the excellent Detectorists and The Thick of It and were in the forefront of showing Scandi noir e.g The Killing and thrillers such as the French Spiral. You can currently watch some of these on iPlayer or the subscription service Britbox.
In terms of commissioning and buying new content, with funding cuts the BBC will increasingly struggle to compete. Well done, Johnson stooge Nadine Dorries. So long as you have Netflix, eh?