Is there any registry / setting that control the feature manager “width”
I am using feature manager that is “docked” beside the feature tree.
However, when i start using SW2020 recently, the feature manager “width” then to get very wide, even if i resize them, when I restart the Solidworks it get reverted back to the wide size. 
Feature manager width is controlled per document i.e. it can not be controlled globally. So I had created a program to keep the feature manager width to certain value. Unfortunately that program is lost due to hard disk issue.
But you can use/try the macros from following links
https://www.cadforum.net/viewtopic.php?p=19980&sid=1bde2bc2acae6d073cb7304c527bb450#p19980
https://www.3dcontentcentral.com/Search/macro.aspx?id=819204
https://help.solidworks.com/2020/english/api/sldworksapi/change_width_of_featuremanager_design_tree_example_vb.htm
Thanks alot
A macro will do too
Cheers 
Or size it in template
Well… this is the weird part…
It IS properly size in our template created in SW2016
When creating part in SW2019 using our template, the PropMgr window appear OK
When creating part in SW2020 using the same template, the PropMgr window got messed up
Don’t tell your VAR, he’ll most likely tell you it’s an issue with your template not being up to date.
It’s fixed in 2023
This is same with 2019SP4. Docking the Feature(Property) Manager will cause it to grow throughout the session. I vaguely recall some discussions on the old forum about it being a bug. No, I’m not going to try to find them. I just remember because we had the same problem early in our blunder into SW and I looked it up then. Most of the users dock the Feature Manager so that the Design Tree isn’t hidden (moved and collapsed automatically at start of feature command). I toggled back and forth for a while, also tired the macro that would auto expand the Design Tree and finally gave up and now the Feature Manager is floating off the left side of Solidworks main window. It’s a bit of pain, but the Design Tree stays put, doesn’t autohide and the feature manager doesn’t take over the viewport after a couple hours of use.
Mentioned here by Jim Wilkinson:
According to that post, it was fixed in SW 2018 SP3 (it wasn’t)
I recall more screen shots about it and talk of a macro to automatically expand the Design Tree when it pops out (which reduces the need to dock the Property Manager), but maybe I’m just not seeing it in the thread there.
The Knowlege Base shows the SPR number 495883 as implemented, but as you stated it’s not. Or it odd number year team didn’t get the memo from the even year team, so it was unfixed in 2019.
Yes, I couldn’t find the original post. Only that one.