Thank you guys. Weirdly enough, a new update message popped up this morning, which I followed through, resulting in adjustable panel size. But when I checked the version, it turned out version 188.8.131.5296 downgraded from 184.108.40.206644. Now when I press 'check update', it pops up the 220.127.116.11644 version available again. Seems like I got stuck in the middle of Möbius strip.
It was good and free to adjust the left panel throuhgout the versions prior to 4.6.4. Now it's not only fixed but fixed wide, taking aweful empty space. Any workaround out there or should we wait for the next version hoping the issue will be gone?