As the others have said, you need to unzip the file first (Itch's uploader randomly - and for reasons no-one can decipher - packages APK files in zip format).
This will walk you through it:
https://support.google.com/files/answer/9048509?hl=en-GB
Viewing post in PUBLIC RELEASE - v0.17.8b - COMBAT AND CONQUER! comments
Thank you, I am leaving the comment in case the issue comes up for future people but I ended up being too excited and before anyone could respond I bought a Patreon membership and downloaded from that link and it went through just fine. (Shocked it was only $1-$5, I was hesitant because most I've seen are like $20/month and I just started a new job.) But thank you for your attentiveness and work with the game.