A Windows PC software is pushing its app onto my android devices. How can I avoid it?
You (or someone else) probably accidentally click this banner on the main screen.

And &quot;Accept&quot; the offer.

(Note: this dialog may also pop-up on reboot)
- OR -
Avast pushed the installation silently (which I still doubt since it didn't happen on my case).

Avast gets the Google accounts saved on the Chrome, and it's possible for them to offer their products on connected devices.

Hello,
Thank you for contacting our support center with your concerns.
We have got it from your Chrome account. If you are signed (permanently) to your Google account in some web browser, Avast can read your devices added to this account and offer our products. This situation can't be blocked.

(Source: Google Forum)
Additional reading: &quot;How did Avast get my Google account info and install itself automatically onto my phone when I hit 'accept' on the desktop app?&quot; on Reddit.