I wanted to know that is it somehow possible to save data in data base from one app and fetch it in another app? If no, is there any other way to connect 2 apps?
Yes of course, as long as your database is accessible to both apps (online/local server)
please tell how. i want to know the process. how can i make it accessible to both apps?
There is no single method, it depends on which database you choose to use and how you want it to work. I suggest you search this forum for:
Google Sheets
Firebase
MySQL
tinyWebDB
php tinyWebDB
CloudDB
php sqLite
to learn more about online database solutions
1 more issue is that app inventor says that there is some internal error, what should i do?
Start a new topic for that one