The Nextcloud App (Not the Memories Nextcloud app) allows taking a photo that goes directly to the server. It's also got a Scan document feature that I use to scan to a Paperless folder for processing.
If you don’t trust your OS, how can you trust it to run an app? Apps can’t hide data from the OS that’s running them.
I’m concerned about what the OS is doing in accordance with its privacy policy or terms of service. Without having read them (I am only human) I assume the photos in the default location are sent off for analysis to “improve your experience by showing you relevant advertising”. I would be surprised if this above-board surveillance went as far as crawling the filesystem