As you might have noticed, the Matomo Mobile 2 App has disappeared from the Google Play Store. We are currently looking into the reason for this and will inform you when we know more.
If you want to install the app in the meantime, you can download the APK files from Mobile App FAQ - Analytics Platform - Matomo
You can also add
https://matomo-fdroid.lw1.at/fdroid/repo?fingerprint=E17D3E831EBFFBF60831FCA36A615769B31E3D1168A173F3CD9EA2FC29DF74D2 as a package repository to F-Droid (a FOSS app-store) to automatically get the latest version.
The iOS app is unaffected by this.