D&D's 5e SRD was released under CC-BY. It only includes one subclass per class and a handful of monsters, but it's all the rules.
Tales of the Valiant and Pathfinder 2e both have SRDs licensed under the ORC license and are based in D&D-type gameplay.
FATE is a different type of TTRPG that has a SRD licensed both under OGL and CC-BY.
Powered by the Apocalypse is a different system and has a permissive, but hand-wavey license.
Of all of these, ToV is the most like 5e without being controlled by a multi-national, public company.
Nah. They'll sell in a leveraged buy-out, which will give the shareholders at Hasbro tons of money, cost Tencent nothing, and put the new D&D LLC in tons of debt. Then they'll piecemeal out any IP or assets that can make them any money before letting D&D LLC go bankrupt. See what happened to Toys R' Us for a past example.