The problem with Mass Effect as a TV show is that it would take an absurd amount of money to do justice to the material. The scale and scope of the trilogy would be an expensive undertaking to realize on the small screen. Obviously, a lot of the side quest stuff would get cut for time or pacing. The other issue comes down to narrative decisions. What worked well in a game may not translate to the screen very well. Finally, given the personal sense of ownership people have over their version of the character, the fan base may be overly critical. Even choosing a gender for Shepard alone would be problematic. Some 84% of Shepards were male initially. Then again, the FemShep crowd is among the most rabidly obsessed with the series.
It's easier to do something like this with the Witcher as Geralt fits a certain basic description regardless of what the player does with the character. The gender is set and you can't change it. Stories set in the Mass Effect universe could work, but they'd really have to steer clear of the game's main narrative, which has its own set of challenges.
Being in a post 2021 world, the Shepard will absolutely be a FemShep. That isn't bad because I like both my characters equally, but fact is more people think of Shepard as male.
The main problem with games is story is often told through environment, like reading or listening to subtle conversations as you pass by. I don't recall how much of this was in Mass Effect but I will say they were overall more straightforward. But this flow of narration is typically the thing that doesn't translate well. There are other aspects like combat and other gameplay sequences. This often helps pace story in a video game, but in the absence of gameplay the pacing might be off. Examples would be fighting through a tough section of gameplay which makes reaching a certain story sequence have so much more weight. Remove that and the scene will still have an impact but it won't be as strong and will feel more like a generic moment.