I've RTFM but to me seems a bug.

Folder paths to monitor ([folders]), is shown only if glances is run from CLI.

I have

[folders]
folder_1_path=/var/blabla
folder_2_path=/var/log

This is what I get, as expected, running glances from CLI: [fs] + [folders]

This is what I get when running in -w mode: only the [fs] is shown

In https://glances.readthedocs.io/en/latest/aoa/folders.html says

in client/server mode, the list is defined on the [server] side.

but this is not clear.