TikTok supports portrait input and for certain users also landscape input.
Portrait Input:
Use one of the portrait resolutions in the Loola Desktop, or set your RTMP accordingly.
Recommended resolutions: 608x1080 or 720x1280
Bitrate: 3500 Kbps CBR
This is TikTok showing portrait input:
Landscape Input:
Landscape input is supported only for users who have "3rd party streaming" option enabled in TikTok.
Recommended resolution: 1280x720
Bitrate: 3500 Kbps CBR
This is TikTok showing landscape input while phone is held vertically:
This is TikTok showing landscape input while phone is held sideways:
Switching from portrait to landscape on the TikTok app: