I tried filing a bug multiple times between both Firefox and Chrome, and always got the the spinner spinning endlessly.
After reading the last post in this thread I tried only selecting one UE4 version in the version dropdown, and the bug was sent successfully.
https://forums.unrealengine.com/unreal-engine/feedback-for-epic/1675435-unreal-bug-submission-form-isn-t-working-anymore
Previously I was selecting the options “4.26” and “4.25 Plus”
Browsers: Firefox and Chrome
OS: Windows 10
No file attachments attempted.
Timezone set to GMT +1, and system language Swedish. The bug reporter URL ends with ?language=en_US