Probably because of how saves and ren'py works.
If you're concerned, feel free to check the script files in the PC version (all of them are left unpacked) and rebuild it into an APK of your own to confirm.
You should just be able to run the game.
If it can't run, try downloading it using another method that isn't itch.io, such as https://gofile.io/d/nWaoiL
That error likely means you need to redownload the game. Itch.io has an issue where it corrupts downloads a lot. So redownload it via itch or the link provided.
The tutorial teaches you to hire employees and buy buildings, and tells you to continue doing so.
It also introduces you to upgrades later on.
So, the way to play the game is to purchase buildings, then hire employees to fill them whenever you are able to. Buying buildings and staffing them is top priority.
Buy building upgrades (and lastly global upgrades) if you can afford it and still make the next payment.
Be as greedy as possible. It's OK if some employees are unhappy, as long as every position is staffed.
When switching employees, use the green arrow icons to check which employees would fit better in the role.