Sketchfab model embeds are supported in Tumblr posts.
Step-by-Step Guide: Embedding Sketchfab Models on Tumblr
Copy the Embed Code from Sketchfab
Go to your model page on Sketchfab and copy the embed code.
Create a Text Post in HTML Mode
Create a new Text post on Tumblr.
Click the Settings (gear icon) in the top-right corner of the post editor.
Set the Text Editor setting to HTML.
Paste Code and Post
Paste your copied Sketchfab embed code into the post body.
Click Post to publish.
Important Notes:
Feed vs. Profile Display: Your interactive 3D model will not render directly in the main Tumblr feed while users are scrolling, but it will fully display and function on your primary Tumblr profile page.
Avoid Switching Editors: Do not switch back to Markdown or Rich Text mode after pasting your embed code, as doing so may break the iframe code. If you need to write additional text in another editor mode, finish typing it before pasting your embed code in HTML mode.