Theia AppImage runs, but inaccessible in browser

[AgyarJanos]

Using TheiaIDE.AppImage --port 8182 --hostname 0.0.0.0 or a similar command, the IDE starts right up. Theia appears to be listening on the specified port, but all I can see in various browsers is the logo image. The browser-based IDE never appears. If I refresh the page I see messages like this in the console: 2024-03-05T21:11:45.243Z root ERROR refused an http request: 127.0.0.1

Also, running without the command-line arguments does not start a server on port 3000.

I've tried installing Theia via other methods, but everything fails at some point. Using Linux Mint 21.3.

I strongly suspect I'm missing something obvious. Any help would be appreciated.

[AgyarJanos]

Possibly relevant issues in Firefox (this time with port 3000):

Uncaught (in promise) TypeError: window.electronTheiaCore is undefined

POST |  
scheme | http
host | localhost:3000
filename | /socket.io/
 
EIO | 4
transport | polling
t | OuGadju
sid | uXRB3M8EfII1Hz2WAAAC
 
Address | 127.0.0.1:3000

Status
400
Bad Request`