Gaps in your layers between walls and infill may be due to linear advance. Linear advance or K value is set at marlin default of 0.22, however myself and a number of other users have tested and found a k value of 0.08-0.1 to be much better.
I copy below a message I sent to another forum member on how to calibrate for K value:
"As of this moment it is a slow process to calibrate K value but possible if you have the time to do it. I used the gcode generator at this link to make a test file https://marlinfw.org/tools/lin_advance/k-factor.html
Unfortunately as the SM2.0 currently doesnt respond to M900 Kx.xx commands, you cannot use the gcode generator above to automatically test multiple K values at once. However, it is still useful as a test print. Because of this, it does not matter what k values you set using the generator.
Once you have the g-code generated, try printing it. This will be done with K0.22 as this is the SM2.0 default. You can evaluate the print performance with reference to the visual guide at this link https://marlinfw.org/docs/features/lin_advance.html.
Once you have determined whether you need to increase or decrease your K value from the initial test you will need to change the setting on your printer before running the test again. To do this, connect to the printer over usb. Once connected, type into the command line M503. This brings up the printer saved settings and you should see one of the lines says M900 K0.22.
To change your K value type into the command line M900 K0.xx (I suggest jumping right to K0.08 as this is what I found was the best setting). Type M500 to save this value. Restart your printer by power cycling and re-connect over USB and type M503 again to double check your new K value has been set. Now re-print the g-code and re-evaluate.
Rinse and repeat until you are satisfied that you are printing consistent line width!
Hope this helps."