You've already got the answer that LGPL libraries can be used in commercial software. So far, so good. There's more to this than meets the eye, though.
The thing is, PySide2 is for using the Qt framework with Python programs.
Besides the LGPL license for PySide2, you'll have to make sure that you comply with the Qt licensing terms.
The Qt licensing FAQ lays out your options:
- You can get a commercial license which allows you to do everything with Qt with no concerns about opensource.
- You can use only those parts of Qt that are under the LGPL and have no concerns about opensource.
- The third alternative is to go with the GPL license, which will require your product to meet the GPL2 or GPL3 terms.
There are some portions of Qt that are only available under the commercial license. There are differences in the available modules between LGPL and GPL licensing.
You'll need to look at which Qt modules you really need, and see which license fits your needs.
Since you want to keep your proprietary code under a proprietary license, your only options for Qt are to use the LPGL version or buy a commercial license.
As I understand it, the commercial Qt license is expensive. I just checked, and a 1 year subscription for a single developer is currently over $5000.
I use Qt in my personal projects, but they are all under the GPL so I can use the GPL licensing on Qt and not have to pay for a commercial license.