Update 18 August: Apple has today released beta 5 to developers, with the release notes stating that “VoiceOver is now functional.”
Update 10 August: Apple has today released the Public Preview of watchOS 7, and it appears that it does indeed not work with VoiceOver as was the case with last week's developer release.
Apple's Beta Program page for watchOS 7 currently carries the following warning:
“Please note VoiceOver isn’t functional in watchOS 7 beta 4. If you rely on VoiceOver, don’t update to watchOS 7 beta until this issue is resolved.
Apple has released watchOS 7 beta 4 to developers; with the release notes warning that VoiceOver users should not update:
“VoiceOver isn’t functional in watchOS 7 beta 4. If you rely on VoiceOver, don’t update to watchOS 7 beta until this issue is resolved. Enabling VoiceOver in watchOS 7 beta 4 might also cause a significant battery impact.”
If you have installed a previous beta version of watchOS 7, we recommend that you temporarily remove the watchOS beta configuration profile so as to prevent the automatic download and installation of beta 4.
The watchOS 7 beta is currently available to developers only, but for the first time ever, Apple is also planning on a public beta of watchOS. Apple had originally said that this would be released in July, but this did not happen and Apple’s Beta Software Program website still lists the watchOS 7 public beta as “coming soon.”
Accordingly, it's possible that Apple may release beta 4 of watchOS 7 as the public preview. If this is the case, people intending to take part in the Beta Software Program need to be aware that once you update to watchOS 7 beta, the only way to downgrade back to watchOS 6 is by sending your Apple Watch to Apple, and that this service is only available in selected countries.
If you have access to the watchOS 7 beta, either through Apple's Developer Program or the upcoming watchOS Beta Software Program, we strongly recommend that you do not install a beta release until there is confirmation from Apple in release notes that the issue with VoiceOver has been resolved.