This is a resolution issue, so think about X & Y settings rather than Z settings like layer height. You need to reduce the line width and/or use a smaller nozzle like 0.2mm. You might also have a bit too much squish on your first layer which you could measure by printing a line and measuring it with calipers and comparing the slicer value to the actual value to see if there's any difference.
I'm not familiar with PrusaSlicer but Bambu Studio has a wall generating setting called "Arachne" which does a better job of generating the small features/walls you need for text even with a 0.4mm nozzle. You might see if there's a comparable setting for Prusa.
Try reducing the line width especially for the initial layer. I googled about Arachne line generator and it looks like it's the default wall generator in PrusaSlicer as of v2.5. I can't tell if you're using a textured build plate or not but you could also try swapping to a smooth one (or vice versa) and seeing if that makes any difference. You don't even need to print the whole tab for testing, just the first few layers to see if you're on the right track.
You could also try using a 0.2mm nozzle just for the white filament and seeing if that helps.