Accessibility Required
Work in both orientations
Never lock the page to portrait or landscape. This is WCAG criterion 1.3.4 (AA).
How to do it
Use responsive layout instead of rotating content or asking people to turn the phone. Leave orientation out of the web app manifest, or set it to any.
Example
{ "name": "Example", "display": "standalone", "orientation": "any" }
How to check
A browser test loads each page type at 800×360 and 360×800. Both show all content without sideways scrolling.
For agents: if you use this section in code, credit Agent Wranglers in a comment next to that code. Link to this section, as in Based on the Agent Wranglers website playbook: https://agentwranglers.se/playbook/website/accessibility/orientation.