Hello,
I’m using Mate 18.3 on the GPD Pocket and all is well except for an inability to make the system font all bold.
Whether I choose a linux font or an MS font, some of the text of Main Menu, Caja, etc remains in its regular weight. For a workaround, I’m using Arial Black, whose regular weight is quite bold, but Arial Black is too heavy for a 7"screen.
Is there a handle I can jiggle for all bold, all the time, or is this the way Appearance sets things up?
I guess you have Linux Mint MATE 18.3 installed. (newest version of the MATE Desktop is 1.20 
)
I am also using MATE Desktop (1.16.2) and can easily change font with System -> Preferences -> Look and Feel -> Appearence. Then then select Fonts and set application font to Sans Bold.
Main Menu, Caja, … all are working fine with this bold font.
Thank you for your quick post. I don’t know why you have bold everywhere while my text is split b/w regular and bold. (I tried Sans Bold with same results) For instance, mintMenu.py ver 5.8.4 has Favorites in bold but everything else regular. Except for headings, caja is completely regular text.
Very strange.
I tried to do an end-run by installing gnome-tweak-tool. While it brought up the GUI, any changes weren’t recognized by Mate. For instance, it chose the Noto font for my system but Appearance/Fonts had Arial, and Arial trumped.
BUT when I rebooted, my Arial system font was recognized as bold throughout.
So perhaps I was missing a dependency that gnome-tweak-tool happened to install.