Friends, my suggestion is, to immediately backup your installed applications following this guide
https://tinyapps.org/blog/202009280700_backup_ios_apps.html
Unfortunately Apple removed officially from iTunes 12.7 version to backup apps, only data is stored.
But using iMazing you can extract the app data and download and Export the app itself as an IPA file.
Also you can download a previously purchased app via this method, if the last (but considered old) version of the program is still on iTunes Store.
https://imazing.com/guides/how-to-manage-apps-without-itunes