That's my assumption. I doubt there will ever be an official cancellation, just a refusal to acknowledge developmental status and prolonged periods of silence during which they hope Metroid slips out of the public consciousness. Then we'll get a reboot a decade from now just called Metroid.
To be fair, MP4 hsa had plenty of development hell.
The original dev team working on the project had everything scrapped as Nintendo brought back Retro Studios to work on the franchise; so the original build is long gone.
Covid came around and slowed production.
All of that happened in 2019.
And it is only now getting into 2023. If Retro Studios had to build the game from the ground up, they may have some internal conflicts on story development as it is likely they would be making a hybrid of the original script of MP4 and their own revision draft of it.
Add in whatever engine they are using. Are they using a pre-built one or are they making serious upgrades to the engine of MP3: Corruption?
Honestly, I would expect some sort announcement at least at the Nintendo Direct that is supposedly supposed to happen this month. Something to show that three years of progress, whether it be a development trailer or a cinematic teaser.