Some OnePlus 8 Pro handsets have been downgraded to DRM Widevine L3 by a recent OxygenOS update. There is no fix in sight despite being confirmed by OnePlus and fans have been voicing their dissatisfaction about it.
https://www.notebookcheck.net/OnePlus-8-Pro-DRM-Widevine-L3-issue-confirmed-by-OnePlus.464927.0.html