Your system has been infected by STOP/DJVU ransomware. STOP/DJVU ransomware variants after August 2019 are only decryptable if an offline key was used. For variants with an online key you cannot decrypt files.
That means your variant is not decryptable.
Your options without a backup:
1) Recovery: In rare cases ransomware fails to delete shadow volume copies or fails to delete the original files properly. You can try to recover files via shadow volume copies and file recovery software. 2) Repair: Certain file types, mainly video and audio files, can possibly be repaired with tools like MediaRepair. But these files will loose some data. 3) Wait: Backup encrypted files and a ransom note and wait in case a solution comes up later. Maybe law enforcement gets hands on the keys or the criminals publish the keys as it happened with, e.g., GandCrab. I suggest reading the news on this. Emsisoft will update their decrypter if that happens. 4) Pay: There is the option of paying the criminals, but we highly recommend against this step. You will just fund later attacks. You may also pay without getting your files back. These are criminals and as such not trustworthy.
Please let me know if you need help for the steps 1) or 2)
Make sure the correct drive letter is selected (usually "C:" )
There is a date on the upper bar. Check if there is a date available that was before the ransomware attack. If the date isn't available, you don't have any shadow volume copies from before and recovery is not possible.
Within Shadow Explorer, navigate to files or folders you want to recover
To recover: Right-click and click Export... then choose a folder to save the files to and click OK
That means you have no shadow volume copies. Ransomware often deletes them. You cannot recover with Shadow Explorer in this case.
If you haven't tried already, see if you have success with any of the following:
1. File Recovery Software
Please download PhotoRec, choose Windows 64-bit from that list.
Right-click on the testdisk-7.1.win64.zip archive and click Extract all.
Now navigate into the extracted folder and run qphotorec_win.exe
Select your Hard Disk from the list.
Make sure that FAT/NTFS/HFS+/ReiserFS is selected
Choose a destination for your recovered files by clicking on the "Browse" button
Now click "Search" and the tool will start recovering. Wait for it to finish, then click Quit
You will find recovered files in the selected destination folder.
If you had any external drives encrypted, you may try the same on them.
2. File Repair
The tool can repair 6 file types: MP3, WAV, MP4, MOV, M4V, 3GP
If you have such files encrypted by STOP ransomware, download and run MediaRepair.
For most file types, you need a reference file, that is a non-encrypted file of the same file format as the encrypted ones. Video files will need this reference file. File types like MP3 do not need one.