(written from a Production point of view)
ViacomCBS, sometimes written as Viacom-CBS, is a corporation which is formed by the remerger between Viacom and the CBS Corporation, they themselves having been the result from the 2005 split of the original Viacom. Formally announced on 13 August 2019,  the remerger was officially effectuated on 4 December 2019 after the obligatory approval by regulators had been secured.  ViacomCBS is a publicly traded company, but a "controlling interest" (an industry euphemism for de facto ownership) continues to be held by National Amusements, just as it had with the two former separate entities, as well as their preceding entity.
While the remerger has in essence all the hallmarks of the resurrection of the original Viacom, there is one major difference; Viacom subsidiary Paramount Pictures did not get back the television division it had lost in the 2005 split. This might seem like a hindrance to a "reunified" Star Trek, but the conglomerate has apparently foreseen that when it already instituted an overall "Star Trek Global Franchise Management" in 2018,  made formal in May 2019, prior to the remerger.