There have been endless speculations about the origin of Bell Beaker.
One line of argument by Dutch archaeologists was very persuasive for a long time. It traced the origin through Corded Ware
(which also has cord-impressions) and Funnel Beaker
(with a large everted lip) to Swifterbant
pottery which has a similar shape to Bell Beaker, but a pointed bottom. However we now realise that
1) Swifterbant pottery is derived from the earliest pottery in Europe, of the Elshanka Culture, which appeared in the Samara region of south-eastern Russia (on the Pontic-Caspian steppe) about 7000 BC. It was made by hunter-gatherers, and is quite different from the pottery that arrived with farmers from the Near East. It influenced Sredni Stog pottery. See D. Anthony, The Horse, The Wheel and Language
(2007), pp. 148-9, and fig. 11.7 on p. 242.
2) Bell Beaker is the same age as Corded Ware and so is not derived from it.
3) As you say, some Yamnaya pottery was decorated with cord impressions.
This explains why we find cord-impressed pottery, both Bell Beaker and Corded Ware, and pottery shapes with large everted lips (both Funnel Baker and Bell Beaker) appearing in far distant places, but in each case there is a trail back to the Pontic-Caspian Steppe.