In the version of Maxthon 7.3.1.7000, the side panel works normally open and closes. See video - 7000.
In the version of Maxthon 7.3.1.7600, the side panel opens, but does not close, does not return to its original position. See video - 7600.
Need to fix.
P.S. I use Windows 11 Pro 23H2 , Maxthon 7.3.1.7600 x64 Portable