You can configure samba to handle the permissions, but immich will need to connect to the user's share using their password (no ideal)
In smb.conf for each user's share
[user_media]
path = /path/to/user/media
valid users = username, immich
force user = username # This makes all files. appear as owned by the user
force group = media
create mask = 0660
directory mask = 0770
Alternatively you can use setguid with your media group:
chmod g+s /path/to/media/dirs
chown -R :media /path/to/media/dirs
chmod 2770 /path/to/media/dirs. (2 = SetGID, 770 = rwx for user and group)
Any new file created by Immich will automatically belong to the media group
The SetGID bit ensures files inherit the parent directory's group
All users (including Immich) can read/write files as long as they're in the media group
Individual users still "own" their files (UID stays as the original user when they upload via Samba)
You can configure samba to handle the permissions, but immich will need to connect to the user's share using their password (no ideal)
In smb.conf for each user's share
Alternatively you can use setguid with your media group: