In the first Thor movie, we see Odin enchant the hammer with the whole “Whosoever holds this hammer, if he be worthy, shall possess the power of Thor” thing. This would seem to indicate that prior to this happening, anybody could have lifted the hammer. Also, this explains why Hela was not only able to hold Mjolnir, but destroy it. It was no longer under the enchantment because Odin had just died.
Article source: https://www.cinemablend.com/news/2480215/thor-love-and-thunder-theory-does-jane-foster-not-need-to-be-worthy-of-wielding-mjolnir