1. Open the JBMod folder (browse local files).
2. Enter the "jbmod" folder.
   
3. Enter the "cfg" folder.
   
4. If the file "autoexec.cfg" exists, open it in notepad.
   If it doesn't, create it. (If you don't see .cfg files, you might have extensions disabled on your system.)
   
5. Paste the following at the end of the file:
   
   sv_allowupload 1 sv_allowdownload 1 cl_allowupload 1 cl_allowdownload 1 cl_downloadfilter all cl_playerspraydisable 0
6. Save the file, now you can close the file explorer.
   
7. Done, now you can normally see and use sprays!

The game's VPK has its own autoexec.cfg which disables these values to avoid some sort of exploit(?)

引用自 STRESSED CAT IN A BOX on Discord：

this is because JBMOD’S VPK FILE already contains an autoexec that DISABLES IT if you don’t have your own autoexec file

Thanks Stressed!