Downloaded apk not installing

I saw that today. I am trying to install it is not installing. Phone is a Xiaomi Note 9 Pro.
Is that happen only me or is that a bug?
And i want to see download to check my computer but they are sending a link to mail. Yes it is good but i think it must to be another option to download to computer.

Is this the first time you are installing this app to your smartphone? If yes, make sure you have assigned an app bundle ID in the app’s settings in Thunkable. If it is an update to an existing app, make sure you have incremented the version code in the app settings in Thunkable. Also feel free to share woth us a screenshot of the issue.

It is not first time but one second i updated firmwave.I deleted old app after than that installed interesting thanks.

Correct. As stated before, your were most probably trying to update an existing installation with an app carrying the same version code. If you had incremented the version code and version name in your new version, it would have updated fine on your device.