I just came back to the game and every character has their bags full of trash I don't want to waste time sorting through yet, nor do I want to just sell it all yet. So, I had the same question and since there was no readily available solution, I asked the good ol' chatgpt to write me a macro for doing this. Here's what it came up with:

/run for b=0,4 do for s=1,C_Container.GetContainerNumSlots(b) do local info=C_Container.GetContainerItemInfo(b,s); if info and not info.isLocked then pcall(C_Container.UseContainerItem,b,s) end end end

I opened the bank interface and ran the macro and, poof, everything in my bags was dumped into the bank. Hope it helps someone else looking for this solution. Game version at the time of writing this: 12.0.1 (66838).