S7 Edge stuck on loading screen with Samsung logo I have used my S7 since 2017. Then I got another phone. After three months of being in a box, I tried to power up the S7 Edge. I got surprised as it now is stuck on Samsung logo screen.

Phone was charged and was working before I put it in a box. When I took it out, it would not respond at all, battery was dried totally. Even being charged 100% does not fix the issue.
These are the steps I tried:
1. Wipe cache partition
2. Master reset
3. Safe mode
4. Reboot to bootloader

All of them do not work, phone is always stuck with Samsung splash screen. When I enter the Volume DOWN, Home and Power key menu, I see the message:
Installing System Update (stays for several seconds), then it shows error. After that I enter Android recovery.

Phone responds to charging normally. It has that animation showing power percentage when its turned off.

Any advice as what program and what I need to do to restore the phone so it can boot is more then welcome :).
It's been a while since I last owned a Samsung, but my best guess would be to try and flash a new ROM using Odin. Here's a link that explains how to do this.
https://forums.androidcentral.com/ambassador-guides-tips-how-tos/499009-guide-samsung-how-flash-stock-rom-via-odin-new-interface.html

on Sammobile, you'll find the original Samsung ROMs, which are normally safe to flash as long as you pick the correct one for your device.