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I'm sorry to hear about your issue, but that's not a Sony problem but rather an android limitation, you can move part of certain apps to the SD card, again that's how Google/Android handle it, as they are/were trying to kill the SD card, with that said, if you don't have 500MB free of your internal storage you won't be able to update apps, again, an android restriction, but it has a reason behind it, once you run out of internal storage certain apps and services will start acting up, even android might start crashing.
Things you could do, uninstalled unwanted/unused apps, if you don't use certain preloaded apps that can't be removed, uninstall the updates and then disable them
Thread closed as this has been covered many times:
/t5/Xperia-M4-Aqua/The-8GB-model-storage-only-has-only-1-5-GB-free/td-p/998186/page/12