[Bug]: TypeError: can't access property "from", window.Buffer is undefined

⚠️ 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

Opening Nextcloud an unsupported user agent throws a console error.

Steps to reproduce

1. Set user agent to Mozilla/5.0 (iPhone; CPU iPhone OS 14_6 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/14.0.3 Mobile/15E148 Safari/604.1 (Firefox desktop mobile emulation)

Expected behavior

Redirect according to https://github.com/nextcloud/server/blob/5c7f52f40ead14d7635bc1327cdcede54e5258cc/core/src/utils/RedirectUnsupportedBrowsers.js#L32-L39

Nextcloud Server version

master

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 core/src/utils/RedirectUnsupportedBrowsers.js, especially the referenced lines, and reproduce the issue with the supplied iPhone Safari user agent in Firefox mobile emulation. Trace why window.Buffer is undefined during the unsupported-browser flow. Done means the user is redirected as expected without the console TypeError.