External Drive NTFS Read Only on High Sierra

The drives were not formatted by or because of the update. They were always formatted NTFS and you never formatted them for your Mac. Instead you chose to run a third party app such as Tuxera or Paragon to allow you to use the NTFS formatted drives. When you updated your OS you failed to update these third party apps.

The better solution would be to format your drives for Mac. Caution, before formatting make sure to copy off all the data on them since during format the data will be erased.

macos never been able to write to ntfs filesystem that ability require paying Microsoft royalties

there are third party component which offer the service

How to Write to NTFS Drives on a Mac

maybe the third party component you were using does not support High Sierra

What others have said is likely the case and reformatting drives

will wipe them clean.

emmag18 wrote:

...would be a disaster for my files which are all images written through Lightroom and will not be recognised if they are 'moved' ie deleted and copied back.

...

Not really. If the files are moved, of course Lightroom will show a "?"

for the file. That just means the database in Lightroom is confused.

Right clicking a file or the highest level in the hierarchy should bring

up a menu with locate originals or something to that effect which gives

you file dialog to locate the files.

Best thing I found when I used to use Lightroom, is keep the Lightroom

database file (Library) and thumbnails on the same drive or in the same

directory as the source files. That way, everything is kept together.

The other thing I had done, kept much smaller "Libraries" and add

the smaller ones to a "master". This way, it is easy to keep smaller

"Libraries" intact with their sources in terms of portability and recreating

a "master" is a an easy task.