Want to batch compute lightmaps on all the maps in your maps folder?

Make sure only the maps you want to compute are in your Documents\Trackmania\Maps\ folder.
If you have TMUF installed, your Trackmania maps folder may be Documents\Trackmania2020\Maps\

In Uplay go to:
Games -> Trackmania -> Properties

Scroll down to "Game launch arguments"
Click "Edit"
Add:

/computeallshadows /upgrademaps /fullcheck /useronly /LmQuality=High

and save.

Alternatively you can change /LmQuality to Fast or Default if you want it to go faster and have lower quality. Or use Ultra for maximum quality.

When you launch the game it will automatically start recomputing lightmaps. Just wait for it to finish.

Don't forget to remove the arguments from Uplay, so the next time you launch the game you can play normally!

Just a side note:
Check the "date modified" on the map files, to make sure they all updated at the time you ran the computations.

If the batch fails on a certain map (sometimes it does)... check the UGCErrorsLog.txt in:
Documents\Trackmania\
It will tell you the last map the game was working on when it failed and closed.
Move the map out of the folder (along with any maps that finished), and start again.