iPad Mini 2 not working as expected

My iPad Mini2 (WiFi + Cellular) with iOS 12.5.4 (which has no hardware repairs done since purchase) has the following issues:

- Power button does not lock the iPad however, shut down works (long press)

- Many Apps like MS Teams gets installed; however, cannot join any sessions

- Overall, the iPad is much slower than it used to be

Actions Taken

- Erased All contents and Settings to Factory Default many times upto iOS 12.5.4