While the first three Mass Effect games were all made with versions of Unreal Engine 3, BioWare began using EA's in-house Frostbite engine for all its games after that. The transition wasn't easy—the first two Dragon Age games had been made with versions of the studio's own Eclipse Engine, and according to Mike Laidlaw that change was why Dragon Age 2's expansion Exalted March had to be cancelled. It's also been blamed for some of Mass Effect: Andromeda's problems, due to both the extra work switching engines created and specific areas where Frostbite was lacking related to animations, map sizes, save systems, and so on.
That's why it's significant a producer at BioWare signal-boosted a job listing for an associate technical director by saying, "BioWare is hiring talented programmers with UE4/5 experience! Come, join our team and work with us on the next Mass Effect game!" A job listing for a franchise director (now taken down), described as "the most senior engineering lead on the next instalment in BioWare’s acclaimed Mass Effect franchise", also included a note that "Experience with UnrealEngine4+ is an asset" even though the EA boilerplate at the top of the listing said, "Our teams drive innovation using cutting-edge tech and tools such as the Frostbite engine".
Prolific leaker Jeff Grubb claimed it's Unreal Engine 5 specifically being used on the next Mass Effect, "And this was a choice made by the team putting the game together, which is how it should work." The Matrix Awakens UE5 demo was apparently quite impressive, not that I'd know since it wasn't made available on PC.
While returning to the Unreal Engine's loving arms wouldn't necessarily prevent a future Mass Effect game from suffering all the problems Mass Effect: Andromeda did (it wouldn't liven up a cast of bland companions, for instance), it probably won't hurt. The next Dragon Age game is reportedly still being made with Frostbite, however, as Dragon Age: Inquisition was.
Here's everything we know about the next Mass Effect so far.