Hi IBADULLA_1999
I am Dave, I will help you with this.
1
Restart your PC, then try changing developer Mode to Sideload Apps, does that succeed?
2
If that dos not succeed the second time, click the link below to download a registry file
https://www.tenforums.com/attachments/tutorials...
Right click that reg file and select 'Merge', then confirm the merge.
Restart (not shut down) your PC to apply that change, and Developer Mode should be disabled.