If for some reason you are unable to use Volume Shadow / VSS with Duplicati2 to enable backup of locked files the following list of exclusions may be a good start.
Files who’s names contain: parent.lock
Exclude expression: *~$*
Exclude expression: *__MACOSX*
Files who’s names contain: Current Session
Exclude Folder: System Volume Information
Exclude Folder: C:\inetpub\temp\IIS Temporary Compressed Files
Exclude Folder: C:\ProgramData\Microsoft\Diagnosis
Exclude Folder: C:\ProgramData\Microsoft\Crypto
Exclude Folder: C:\Users\YOURUSERNAMEHERE\AppData\Roaming\Duplicati
This list is a work in progress so check back in the future.
The “\AppData\Roaming\Duplicati” exclusion prevents Duplicati backing up it’s own sqlite databases which for a large backup can be many gigabytes in size.
You can also probably improve performance on any version before May 2020 by running:
create index BlockCountSizeIdx on "Block"("Size");