So I've tried new Gmail design. I couldn't believe it was that ugly and unpleasant to use.
How to roll back to previous normal Gmail design?
New Gmail design:
Update: Users report that the rollback option disappears. See my note ↓
From the settings
⚙ button on the top right of your inbox - the first option is
Go back to classic Gmail.
Note: I believe some day it will be permanent and you won't be able to use the old design anymore. The same as happened with the new calendar.
So keep that in mind.