[Bug]: Theming: SVG gradient breaks PNG conversion

⚠️ This issue respects the following points: ⚠️

• This is a bug, not a question or a configuration/webserver/proxy issue.
• This issue is not already reported on Github OR Nextcloud Community Forum (I've searched it).
• Nextcloud Server is up to date. See Maintenance and Release Schedule for supported versions.
• I agree to follow Nextcloud's Code of Conduct.

Bug description

When using an SVG containing a gradient as the custom logo of your Nextcloud, the PNG file version of the Logo generated for mails etc. is faulty.

Steps to reproduce

1. Go to your-nextcloud.com/settings/admin/theming

2. Under "Logo", upload an SVG file containing a gradient, like this one:
   

3. Let the Nextcloud send a transactional mail (e.g. via inviting a new user)

4. See how the PNG version of the Logo is not present:
   

5. Check via your-nextcloud.com/apps/theming/image/logo?useSvg that the PNG generated is faulty.

Expected behavior

The PNG version of the logo gets generated correctly.

Nextcloud Server version

30

Operating system

None

PHP engine version

None

Web server

None

Database engine version

None

Is this bug present after an update or on a fresh install?

None

Are you using the Nextcloud Server Encryption module?

None

What user-backends are you using?

• Default user-backend (database)
• LDAP/ Active Directory
• SSO - SAML
• Other

Configuration report

List of activated Apps

Nextcloud Signing status

Nextcloud Logs

Additional info

No response

Start with the theming logo endpoint at /apps/theming/image/logo?useSvg and reproduce the issue using an SVG containing a gradient uploaded through the admin theming settings. The work is done when the PNG generated for transactional mail renders the gradient logo correctly.