Enhance app inventor apk security

Good evening,
I have recently developed a basic app that works as a calculator (it runs some specific equations but nothing else).
I wanted to upload it to Play Store as I think it may help some people in their jobs. Nonetheless, I wouldn't want that this app be harmful for its users due to having a weak security coding (I mean, I wouldn't want that some hacker uses my app to introduce a malware or changes its code or whatever).

I only used the block from MIT app inventor, without any external extensions.

Thus, is there any way I can enhance my app's security?
I have read about Proguard and Obfuscation but I don't really know how to use it or even if it can help with my concern

Thank you in advance for your time

Your app is well protected in the Play Store. Unless you publish your keystore publicly, no one will be able to change/customize your app in the Play Store. Of course, someone can download the APK, decompile it, then customize it and publish it again in the Play Store as their own (new) app under a different packageName. But this possibility always exists and can probably hardly be prevented.

Thanks so much for your rapid responses!