Your server is only one version behind the current one so I'd imagine it will update soon. Maybe your server admin @admin can help?
(The full text search feature is brand new, so it's only available on the latest version.)
For apps it's up to each developer. On Moshidon perhaps @moshidon might have news on adding this setting to the app?
@feditips @mjr @jonny @admin It's already available in the current nightly version, and will be available in the next stable release.
Thank you for liking #Moshidon!