As a player, when I see another player constantly getting talked over, and it’s obvious they’re trying to contribute, I’ll interject the talker (between thoughts, not interrupting) and ask the player being talked over what they’d like to do.

Now if it’s a shy player rather than one being talked over I might instead quietly ask them privately instead, then pipe up towards the GM with “hey, they say they’d like to do this” that way they’re not sitting there with an uncomfortable spotlight on them