The One Connect cable has a bandwidth of 75gbps according to the product page, while hdmi 2.1 spec is 48gbps. So it is technically possible, based on the I/O of the tvs.
That said, Q9FN (2018 QLED)
already supports eARC and VRR. So the current One Connect box is probably sufficient for HDMI 2.1 features. The Q9FN can't do 4k at 120fps, but that is probably a limitation of the panel technology (not something that can be fixed with HDMI).
That said, you don't need to support every feature to be 2.1 certified, and indeed 4k tvs by definition don't do 8k 60fps. So 4k 2019 QLEDs will probably be 2.1 certified, even if they don't upgrade the features from the 2018 models.
You also have to consider that features, like Dynamic HDR, are subjective. It is really the chipset that does this kind of video processing. The I/O is more incidental, and in that respect HDMI 2.1 is nothing but marketing.
8k tvs will (likely) support every 2.1 feature, because they're going to be so expensive, but that doesn't mean they will have the best picture quality. You still have to look at each tv on a case by case basis.
https://www.samsung.com/uk/tv-accessories/optical-cable/