I've read that you need to keep the lid on the Sunlu S2 slightly open to allow the hot, humid air to escape.  I haven't had mine long enough to have direct experience but printed a couple of the Sunlu S2 lid spacers to try them out.  They all seem to have pros and cons - some easily fall off and most won't stay in place. Some are relatively large and some seem too small and easily lost.  With all that in mind, I decided to design one myself.   

Design Goals:  

1. Needs to be small for fast printing but not so small that it's easily lost
2. Needs to leave a 5mm gap (seems like the most common distance)
3. Needs to press in place on the lower edge
4. Needs to stay in place during normal handling of the lid and spools

I decided that I wanted my design to closely conform to the lower lip geometry to help make sure it was a tight fit. I carefully measured the front lower lip of the dryer and copied the profile into TinkerCad.  I then added enough thickness on the front and back sides for strength and a top part to assure there was a 5mm gap.  For the length, I picked 30mm because it looked like that would be wide enough to provide a good friction fit on the lip.   I printed mine vertical in transparent PETG with a brim.  That way the flow lines on each layer add strength to the ‘clip’.  Hopefully this design meets all the goals above and works for you!  The link to the TinkerCad design is below.

https://www.tinkercad.com/things/lAph5gSxxwt-s2-spacer