Reading this it is does seem Dover will be in the NL next season.
https://www.kentonline.co.uk/dover/sport/dover-athletic-hit-with-points-deduction-and-fine-244591/
I'm not sure quite what grounds Grimsby and Southend have for appealing. Two are going down as EFL competition rules and two coming up. They obviously are desperately clutching at straws, if no one was coming up then yes, but the NL fulfilled their season obligations , what goes on at the bottom of the NL doesn't effect the arrangement at the top of the NL and bottom of the EFL.
Reading the Dover chairman's comments a few weeks back, the NL restarted after a government bail out which guaranteed funds until end of December, on the assumption that crowds would then come back. That didn't happen and the NL asked clubs to continue with loaned money, Dover chairman stated Dover FC has never been in debt and never will get into debt just to complete an irrelevant season with no relegation, ( they were already out of the picture for promotion). He sent their loaned players back to their parent clubs, leaving them with insufficient numbers to complete fixtures, a deliberate policy to force themselves out of playing, hence the penalty and fine.
Edit- recalculation- 24 started NL, Macclesfield and Dover dropped out, leaving 22, two up, two down, plus Dover's return means 23 next season.