Can I add a custom search engine to Safari on iOS 27?

While it might help if the particular search engine was identified, you can check the search engine support documents for the engine if interest as those will usually include Safari extensions info when such is available.

xSearch can do this: https://apps.apple.com/us/app/xsearch-for-safari/id1579902068

Qwant, as well: https://help.qwant.com/hc/en-us/articles/48074998975889-Download-the-Qwant-App-on-iPhone-and-iPad

With no additions or extensions, and if the desired search engine is supported by a DuckDuckGo !bang, you can select DDG as your search and use the !bang to get to the intended engine. With DDG set, you can use !g to get to Google search, for instance.

Also send feedback to Apple: Feedback - Safari - Apple

No, you cannot add a custom search engine to the existing list. Besides adding a bookmark to the custom search engine, you could also create a web app: Turn a website into an app in Safari on iPhone - Apple Support.

Donot_Haveone wrote:

Would still prefer to be able to pick my preferred search engine without Apple's supervision, but this may also help. Will give more feedback to Apple.

Send your feedback to Apple: Product Feedback - Apple

Donot_Haveone wrote:

At the moment, my preferred default is DuckDuckGo without Ai, https://noai.duckduckgo.com/%s, and I am able to customize that on Firefox. I can't add that on Safari. But I never know when I might find a different one I like better, that is not yet one of the chosen few offered by Safari.

Chrome and Firefox and presumably closely-compatible browsers:

https://duckduckgo.com/duckduckgo-help-pages/ai-features/about-noaiduckduckgocom

Ask DDG to add Safari.