It appears as though the Metroid Prime series either all take place before the events of The Return Of Samus, or they're in a separate timeline: https://twitter.com/Doeboy/status/1407468788136689664

We could have answers in Metroid Prime 4 should it not end up being the start of an all new trilogy.

So you can do spoiler markings with comments as well. Either way I guess Samus herself with the Metroid DNA would count as a Metroid to the point where they were featured in Metroid Dread. Makes me wonder how Zero Suit Samus would turn out in such a way if the DNA is not just in her power suit.

At the beginning of Metroid Fusion, Samus gets injected with Metroid DNA, and by the end of Metroid Dread Spoiler:the powers she got from that injection fully manifest and transform her into a human-Metroid hybrid for the final boss fight. While she reverts back to her normal self when that DNA is stabilized by an elderly Chozo you meet at one point in the game, she's still carrying that DNA when you beat the game, so she is technically the last Metroid in existence. Metroid Prime Hunters, and all of the Metroid Prime games, take place in this weird point in-between the first and second sidescrolling Metroid games long before she got injected, so as of now it is the only game in the series to not have any Metroids in it. If you're wondering why the entire Metroid Prime series takes place between the first two Metroid games, I couldn't tell you, but I don't think Metroid was originally intended to have an overarching plot that big.

Admittingly I am confused about if Metroids themselves are also completely absent from Metroid Dread or not.