Can a malicious app access another app's local data

I've been wondering about this for a while. If a malicious Windows app wants to access another app's local data, can it be prevented? I know that many apps nowadays support end-to-end encryption. But does E2EE encrypt local data so other local apps can't access it? Or does E2EE only encrypt data before it leaves the computer so the server can't access it? I guess I'm just wondering how local data access works in general and what are some things …

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