Forward slash problem was caused by a reverse proxy - rollback

strapi/config/admin.ts

@@ -14,5 +14,5 @@ export default ({ env }) => ({
     nps: env.bool('FLAG_NPS', true),
     promoteEE: env.bool('FLAG_PROMOTE_EE', true),
   },
-  url: env('ADMIN_PATH', '/dashboard'),
+  url: env('ADMIN_PATH', 'dashboard'),
 });

strapi/config/server.ts

@@ -7,5 +7,5 @@ export default ({ env }) => ({
   webhooks: {
     populateRelations: env.bool('WEBHOOKS_POPULATE_RELATIONS', false),
   },
-  url: env('PUBLIC_URL', 'https://api.enderman.ch/cms'),
+  url: env('STRAPI_ADMIN_BACKEND_URL', 'https://api.enderman.ch/cms'),
 });