Subject says it - I could not find any option that would do this.
The Source NAT view is not feature complete yet and doesnt replace Outbound NAT yet, it was just there in automation too so it got a quick view overhaul so it looks like the other modern pages.
If something is missing best open a github ticket.
All fine and dandy. Are you planning to continue the work through the 26.1 CE? Or will we have to wait for 26.7 until now unused parts of the UI will be removed and e.g. Source NAT completed?
And what are the plans for the next business edition? As a paying customer I would appreciate consistency and an "all or nothing" attitude very much. For the CE it's ok in my opinion.
Source NAT was in "Firewall - Automation - Source NAT" before. Now it was just moved into the NAT submenu to get rid of Automation. It has been there in the Business Edition for years too.
Regardless it is planned to replace Outbound NAT at some point but there is no new roadmap yet.