Apple CEO Tim Cook has specifically blamed the higher presence of malware on Android devices on sideloading of apps, which Google permits.

Source: https://mybroadband.co.za/news/software/488151-ios-17-could-let-iphone-users-sideload-apps.html

Figure 18: One more variation on the double-dip sideloading theme, with an HP tool in the XLGameUpdate spot at center-top and yet another DLL in the highlighted malicious spot at upper right.

Source: https://www.scmagazine.com/native/threats/a-doubled-dragon-breath-adds-new-air-to-dll-sideloading-attacks

Here is a step-by-step tutorial on sideloading Android apps.

Source: https://www.chiangraitimes.com/tech/how-to-install-chrome-extensions-on-android/

I doubt they would be any looser with sideloading than Android.

Source: https://apple.slashdot.org/story/23/04/17/1725249/ios-17-to-support-app-sideloading-to-comply-with-european-regulations?utm_source=rss1.0mainlinkanon&utm_medium=feed

This modification would prevent users from sideloading specific APK files and would also prevent app stores from installing those same apps.

Source: https://www.canindia.com/android-14-to-block-outdated-apps-to-help-reduce-malware-attack/