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 184.108.40.20696 downgraded from 220.127.116.11644. Now when I press 'check update', it pops up the 18.104.22.168644 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?