There is no option inside of Glide to reduce file size upon upload. Not sure of the best way to handle this for the multiple file/image pickers.
You may need to send this array of images to a service like Make so you can iterate through them, reduce their file size with some sort of image reducer, API, get new URLs and somehow upload them back to Glide as an array using Glide API.
I’ve never attempted this, so I’m not certain if this will work.
The multi-file/multi-image columns cannot be written to directly via the API, but I guess what you could do is write a joined list of URLs to a text column, and you’d then need an action back in the App to write that to the Multiple File column (after coercing to an array). So a very clunky solution, even if it did work