The free "Free" subscription plan is limited to creating one pipeline from Google BigQuery to Google Analytics 4 (via SFTP). For paid subscriptions and during the trial period, this limitation does not apply.
Upgrade your subscription plan
Go to the Project settings page, in the 'Current plan' section click the Edit button.
On the next page, choose the plan that fits your needs most: Starter, Growth, Professional, or Enterprise.
After you confirm the payment method, the pipeline will be activated and you'll also be able to create more than one pipeline.