My cameras are still under warranty. When at the end of the year, some cameras are not updated, I'll return these under warranty.
Web access was a key feature which has been mentioned on the specs which then doesn't work anymore. Therefore that is broken and by our warranty laws, can be claimed.
However, let's first wait what cameras reolink will update before years end.
I would suggest you to do the same if that key functionality is broken for you.

I've found HTML5-firmware for RLC-410W (IPC_51316M), which looks and works great!
However, I'm still missing HTML-5 capable firmware for the E1 Zoom (IPC_515SD6). Can you point me in the right direction, where I can find this firmware?

Original quote of https://support.reolink.com/hc/en-us/articles/900000501023-What-Should-I-do-if-Adobe-Flash-is-no-longer-Supported-at-the-end-of-2020

What Should I do if Adobe Flash is no longer Supported at the end of 2020
Ivy
1 day ago Updated
Applies to: All Reolink cameras that support Web UI

New firmware for web access without using Adobe Flash Player will be released soon before the end of 2020. Our R&D engineers are working hard on it. Once it is available, we will publish on Reolink Official Website immediately. Please pay attention to the information in Download Center.

Thank you in advance for your patience and understanding. Please stay tuned!