richdocuments ignores custom webroot

Describe the bug
I cannot get nextcloud to open files via collabora. Whenever it tries to do so, it completely ignores my specified webroot and thus hits a 404 (it tries to get https://domain.com/custom_apps/richdocuments/... instead of https://domain.com/cloud/custom_apps/richdocuments/...). It's been months since I first discovered this, but it still hasn't been fixed sadly.

I've already tried using a standalone collabora server instead of the app, but no luck there either. The config has

'overwritewebroot' => '/cloud',
'overwrite.cli.url' => 'https://domain.com/cloud'

To Reproduce
Open a collabora document

Expected behavior
It should apply a custom webroot, /cloud in my case.

Client details:

• OS: Arch Linux
• Browser: Floorp
• Version: 11.7.1
• Device: Desktop

Server details

https://hub.docker.com/_/nextcloud/ (the official AIO image is a PITA to set up and has its fingers where I don't want them. Also kinda forces me to test on prod, so I'm not a fan)

Operating system: Arch linux

Web server: Whatever came with the docker image

Database: MariaDB

PHP version:

Nextcloud version: Whatever came with the docker image

Version of the richdocuments app latest, at this point it doesn't even seem to matter anymore...
Version of Collabora Online also latest

Configuration of the richdocuments app

{
    "apps": {
        "richdocuments": {
            "canonical_webroot": "",
            "disable_certificate_verification": "yes",
            "enabled": "yes",
            "external_apps": "",
            "installed_version": "8.2.4",
            "public_wopi_url": "https:\/\/domain.com\/cloud\/custom_apps\/richdocumentscode\/proxy.php?req=",
            "types": "prevent_group_restriction",
            "wopi_allowlist": "",
            "wopi_url": "https:\/\/domain.com\/cloud\/cloud\/custom_apps\/richdocumentscode\/proxy.php?req="
        }
    }
}

POST
	https://domain.com/custom_apps/richdocumentscode/proxy.php?req=/browser/f76e08a/cool.html?WOPISrc=https://domain.com/cloud/index.php/apps/richdocuments/wopi/files/1399_oc2zcelp23cu&title=/foovar.odp&lang=en&closebutton=1&revisionhistory=1
Status
404
Not Found
VersionHTTP/2
Transferred918 B (643 B size)
Referrer Policyno-referrer

Start with the browser request to custom_apps/richdocumentscode/proxy.php and the overwritewebroot and overwrite.cli.url settings shown in the report. Trace how the richdocuments WOPI and proxy URLs are assembled, then reproduce by opening a Collabora document. Done means the generated proxy URL includes /cloud and no longer returns 404.