Fairphone | FP3+ | FP3 | previously on e-4.2-a15-20260816663281-community-FP3 | not rooted
I can confirm the slow download speeds for both FP3 official and FP6 official. DL speeds seemed to hit a ceiling at 500 kB/s (right now they are reaching 1 MB/s). – In the Updater, these would not be offered at all yet.
Surprisingly, FP3 official is available (see above) before FP3 community, making me wonder if it’s a writing on the wall (the long-announced start of retiring FP3-community?) – which also made me a bit reckless and add another chapter to my 
What wiser ones warned you against adventures. I was able to go from e-4.2-a15-20260816663281-community-FP3 to e-4.3-a15-20260917677554-official-FP3 in one go.
Manual installation of the same file through the /e/ RECOVERY was eventually SUCCESSFUL. To get there, I had to accept a signature verification error.
P.S.: The bootloader on this device is unlocked.
Fairphone | FP6 | FP6 | previously on e-4.2-a16-20260815662938-official-FP6 | not rooted
Update did not show yet in the Updater, but succeeded via local update.