Regarding Grimoire
In minigameGrimoire.js lines 409, 413, 487, 488, removing titleFont from their class should suffice
(I'm looking at files in https://github.com/repoclones/neuroclicker-prod/tree/main so line numbers may or may not vary)
As for the left part of the screen the relevant part seems to be on line 14309 of game.js, but the fix is not as easy, as the whole section that the Neuro gain speed is under has the title marker.
Perhaps the unified response to those would be to create new class in css with a desired font family that has more visible numbers when text is small. So for minigameGrimoire.js you would instead replace 'titleFont' with the new class name.
And then for the Neuro gathering speed on left part, you would add the new class, requires a bit of changes in the line as the original one doesn't have class marker by default, resulting in something like this for game.js line 14309 (Hope I didn't mess up there 😅 ):
str = str + '<div style="font-size:50%;" class="newFontClassNameHere' + (Game.cpsSucked > 0 ? ' warning' : '') + '">per second : ' + Beautify(Game.cookiesPs * (1 - Game.cpsSucked), 1) + '</div>';//display cookie amount