Yes, you can fork it and you can do with it what you want. It is even allowed to apply proprietary licenses. See https://en.wikipedia.org/wiki/GNU_Lesser_General_Public_License
But you have to make the code available to your customers if it is a derivative work, so that they are able to modificate it on their own and reverse engineer it, as stated in the link:
The main difference between the GPL and the LGPL is that the latter
allows the work to be linked with (in the case of a library, 'used by') a
non-(L)GPLed program, regardless of whether it is free software or proprietary software.
[1] The non-(L)GPLed program can then be distributed under any terms if it is not a derivative work. If it is a derivative work, then the program's terms must allow for "modification for the customer's own use and reverse engineering for debugging such modifications."
As of the nature and structure of Odoo, whatever you want to do with it, it will almost certainly be a derivative work.
Your question astonishes me after your numerous unsubstantial negative remarks about Odoo.
I hope you astonishes when fabien remove his own tweet and change odoo license too. I had negative remarks on odoo always where it had hell issues or performance, in case we rebrand, we upgrade for better level.
I wish you good luck with your plans and I'm waiting to see your "better level" odoo. But you should speed up your process, because you did ask the same thing 6 months ago and got a proper answer, and after six month you are asking the same question again and get the same answer. With this speed, your "better level" Odoo 9.0 will be ready, when we have Odoo 20.0.
https://www.odoo.com/forum/help-1/question/how-to-fork-openerp-odoo-which-version-best-to-fork-90959
We dont' want better level of odoo, even we believe odoo interface not stand for us, also we had different level of use.
We had newly design interface, complete web front, just openerp 6.1 run as backend, who cares what odoo make in next version and change license, better a small own startup,