Solucionado.
He instalado android studio, bajado android api 28 y en delphi add new sdk, ahora ya aparece la 26.1.1
Y ademas......
Go to the AndroidManifest.template.xml file within your Delphi project directory and then change the "android:targetSdkVersion" from "%targetSdkVersion%" to "26". This is a bug in Delphi. It should be fixed in the next major update.
Also make sure that you have Android API 26 selected withen the Delphi SDK Manager Properties
Un saludo