It doesn't have to be malware. There are also apps around which are region locked or ain't availalble due to GDPR. Diablo Immortal for example isn't available in the store for my country, The Netherlands. That's due to the rules regarding lootboxes. But i can get it through apkpure and apkcombo, 2 trusted sites.
Now as for modded apk's then there are some scamsites around and can indeed end up by installing malware. First off all i would not install modded apk's to your tablet or phone. Next to that turn the automatic sign in to google play services off. I use modded apk's with MeMu. MeMu is just like bluestacks an android emulator, which you can use on your pc. Difference is that in MeMu you can access the storage and move things. I have made one exception though regarding modded apk's, but that's because it doesn't run on emulators. That's for the game too hot to handle from netflix.
Also, pay attention to where you download stuff from. This site is a good source for modded apks. But sites where you have to visit a partnersite (often an advertisement) to get a link, then you know it's wrong.