How to prevent a folder from being synced on OneDrive?

I recently downloaded a very large amount of images for a Machine Learning project. OneDrive is going a little bit crazy about it and I would like it to "ignore" the folder. Ideally, the folder would be isolated from the rest of the synced folders from OneDrive perspective, but in the same directory on my computer.

I tried to navigate through OneDrive > Settings > Account > Choose folders, but as soon as I uncheck the folder, OneDrive says "If you confirm, the folder won't be available anymore on your computer, but only online" which is exactly what I wan't to avoid ...

Any clue ?

N.B : I saw this post How to exclude a specific file or directory from OneDrive within the OneDrive folder structure but the solution doesn't work for folder (and I can't just specify the 200k files that i want to be isolated)

The article Exclude files and extensions from syncing to OneDrive – via Group Policies, by a Microsoft employee on May 5, 2021, describes this undocumented method, which is quite recent in Windows.

The OneDrive sync app must be restarted after this setting is enabled for it to take effect.

Step 1 : Add new policies to the Local GPO store

• Position to folder %localappdata%\Microsoft\OneDrive\BuildNumber\adm\
• Select the files OneDrive.adml and OneDrive.admx
• Copy the files via Ctrl+C
• Position to folder C:\Windows\PolicyDefinitions
• Copy the files to the folder via Ctrl+V. Put the .adml (language) file into the en-us folder, not in the root.

Step 2 : Use the new policies

Now that the new group policies have been added:

• Open Settings > Devices > Configuration Profiles
• Open the new setting "Exclude specific kinds of files from being uploaded" found in Computer Configuration > Administrative Templates > OneDrive
• Click on Enabled
• Click on Show
• Enter the files to exclude with wildcards
• Click OK

Alternative - Use the registry

• Start regedit
• Navigate to HKEY_LOCAL_MACHINE\Software\Policies\Microsoft\OneDrive\EnableODIgnoreListFromGPO
• Create items named by a number( 1, 2 etc.) of type REG_SZ
• Enter as value keywords with wildcards.

For example, enter *.pst to block all files with the .pst extension. Enter expense* to block files that have names beginning with "expense". And so on.

Currently, we can prevent image files being syncing to OneDrive, but we could not could not exclude specific folders to be synced to OneDrive.

Here is a similar thread "Registry exclude folder for OneDrive", on thread "Reassess the possibility to ignore or exclude selected OneDrive folders and files from the sync process." on UserVoice forum, the OneDrive PM Manager said they are are looking to expanding such feature to folders in the future.

I suggest you go to OneDrive folder, then copy the specific folder to other location that won't be synced to OneDrive, then navigate through OneDrive > Settings > Account > Choose folders agian, then unsynchronize this folder.

The folder would be still exist on your local computer, but it is no longer a mirror of the folder with a same name on OneDrive.