App removed from App Store and lost my data

So I’ve been using a free app from App Store to track all my expenses and income the last 3 years, which was taking a backup on iCloud and every time I was reporting my iPhone or bought a new one all my data was easily there.

However a couple of weeks ago I backed up and restored my iPhone in order to gain some free space but that app was not able to download anymore. The app shortcut still exists as an icon in my iPhone with the iCloud icon next to it, however when I tap to download it sais “the app could not be installed”

I searched for it on App Store and it’s been removed since a newer version was out which offers no migration.

Checked my iCloud backups from iPhone and the data is still there (around 450mb) but without any info on it.

Contacted the developer and after tons of emails they replied that the app support has been stopped and they will try to find a solution, however I struggle to believe them.

Contacted iTunes support and they keep replying nonsense as if some robot is answering my emails.

what else would you suggest ?

Is there anyway to re install the app and manage to load my expenses and then try to export them from the app?

I remember with older versions of iTunes I could install the ipa files that were save in my PC but can’t find such an option on current version of iTunes but also cannot find where the ipa files are stored.

What would you guys suggest except from starting using a new expenses tracking application?