You’re right to be reluctant to apply everything by hand. K3s has a built-in feature that watches a directory and applies the manifests automatically: https://docs.k3s.io/installation/packaged-components

This can be used to install Helm charts in a declarative way as well: https://docs.k3s.io/helm

If you want to keep your solution agnostic to the kubernetes environment, I would recommend that you try ArgoCD (or FluxCD, but I never tried it so YMMV).

Any modded app provided for free by some rabdom uploader is suspicious. You cannot blindly trust any platform. If you care about your privacy and your device’s security you should analyze the app’s content in depth or buy the app (or crack it yourself, but it usually means you need to buy the app first).