Apps recently changed, without an update from the store

I've recently noticed that once in every few days, several apps on my phone suddenly show as "recently updated", even though they didn't get any update from the Play Store. The way I can see that they were updated, is not through the Play Store, but rather through Nova launcher's "new/updated" apps category, and also through Total Commander's "Installed Apps" sorted by date. Since it's a Pixel phone, I wonder if that could be due to some Google-related infra/library being updated in the background (just like the Play Store app sometimes auto-updates itself without any notice), or should I start worrying about malicious code slowly crawling through my phone and injecting itself into other apps? A few points worth mentioning: * Phone isn't rooted, and doesn't allow to install third-party apps. * Developer options are accessible, but USB debugging is disabled, and I didn't change almost any setting there. * The Play Store app settings doesn't allow any kind of auto-update unless I initiate and approve each update. * The apps that change/update in each batch seem totally random: they could be of any type, and doesn't seem related to how frequently I use them (some of them I haven't launched in months, maybe a year or more). * Usually, no more than a few apps in each batch - and no more than one batch every 1-3 days or so. * These apps continue to get regular updates through the official Play Store and everything seem fine. * There are still many apps on my phone which weren't updated/changed at all, for some of them the last change/update was more than a year ago. Any ideas on what or how to check this? Anyone else may have noticed similar behavior?