I recently came across the issue that I wanted to setup Unifi Talk but I didn't want to buy a talk device just to set it up (this was the recommended way from Unifi)
For Unifi Talk 4.2.4 its a little more difficult but still possible:
- Go to your Unifi Talk setup page and press right mouse button -> Inspect
- Go to Network tab in Dev Tools
- Search for index-
- Reload the page
- On the new item that just popped up right click and select "Override content"
- It wants you to select a folder so select a empty folder on your pc
- In the file editor hit Ctrl + F
- Search for
internalToolingEnabled: !1 - Replace it with
internalToolingEnabled: 1 - Reload the page
Now you should be able to press the next button even with no devices!
So I began investigating the code and found out that if you press 10 times on the "Setup Device(s)" text you'll be able to skip the device step.

https://ubiquiti-networks-forum.de/wiki/entry/267-unifi-talk-ohne-unifi-phone-hardware-einrichten/
Working with 4.2.11
Same command from link, without escaped quotes and English.
Shell Command
psql -U postgres -d unifi-talk -c "UPDATE config SET data = jsonb_set(data, '{setup_complete}', 'true', true);" && systemctl restart unifi-talk && echo 'Setup complete and Talk Service restarted!'Output
UPDATE 1Setup complete and Talk Service restarted!