Shame on you Figma.... Here is a workaround without having to install a fork
Register the client:
curl -X POST https://api.figma.com/v1/oauth/mcp/register \
-H "Content-Type: application/json" \
-d '{
"client_name": "Claude Code (figma)",
"redirect_uris": ["http://127.0.0.1:19876/mcp/oauth/callback"],