There are already a lot of questions regarding that, but the answers didn't help me and my reputation is not high enough to comment the answers.
I like creating appointments in the the icloud calender by browser. The timezone setting is for USA, but I need the one for Berlin, that is not listed in the select box when I view my account settings and want to change the timezone.
On the iPad and iPhone the appointments I created in the icloud are shown several hours later, sometimes a day later. They contain also the other timezone information, but changing it there for the appointments is not possible. Because when I open the appointment on the mobile device, there is already the desired time chosen (with US timezone information). Only the overview in the mobile calender doesn't take care about it.
In the mobile device settings I have disabled and enabled the option "fixed timezone". This is iPadOS 13.3.
Thank you for a hint.