At Qt Day 2019 in Florence, Italy, I gave a presentation about "Using Qt under LGPLv3".
In the first part, I go through Section "4. Combined Works" and explain the obligations of LGPLv3 in detail.
When you combine your application with the Qt libraries, you can keep closed the source code of the application and publish the application and the Qt libraries under your license terms. You must satisfy the following conditions.
On a physical medium like a USB drive or DVD, you must provide the source code of the Qt libraries, the text of the LGPLv3 and GPLv3, the Copyright notices of the Qt libraries, a description of your modification of the Qt libraries and the installation information. If your application has a user interface, you must display the license texts of the LGPLv3 and GPLv3 and the Copyright notices in this user interface.
The installation information - a.k.a. the anti-tivoisation clause - describes how the user can build a modified version of Qt, how to install this version on the device, and how to run the application with the modified Qt version on the device. If you build a B2B product, you need not provide the installation information.
In the second part, I compare the costs of Qt Commercial and Qt LGPLv3. You must check the licenses for all packages of the (embedded) Linux system, no matter whether you use Qt Commercial or Qt LGPLv3. Qt commercial adds per-developer fees and per-unit fees (royalties). If you use Boot2Qt, Qt for Automation, Qt Safe Renderer or other commercial add-ons, Qt Commercial may well be worth the additional costs.
In the third part, I show how Yocto (bitbake) and Fossology help with the compliance checks. Fossology is a license and copyright scanner.