Dynamic array difficulty: LOOKUP/SUMIF/UNIQUE/FILTER/XLOOKUP based on multiple criteria

I have an inventory spreadsheet. Each entry lists an item code, a lot number, and a quantity. I'm trying to sum up the quantity for each unique [Lot#]*[Item] combination, preferably using a dynamic array because the base data set is large and prone to changing frequently. I can extract totals for each item or for each unique lot#, but some lot#'s are shared by multiple items. I've tried a couple different approaches with SUMIF(), UNIQUE(), XMATCH(), XLOOKUP(), etc. and I'm so close to an answer but I've been looking at it for far too long now and my brain is turning to mush. Id' greatly appreciate any help you have to offer.

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BONUS QUESTION:
CAn you suggest a cleaner approach to populating the tables to the right? I have two different approaches there, one with clonky normal references and one with a separate XLOOKUP in each column. I know there's a better way