Depends on the platform you’re using. Mobile you have the integrated player that doesn’t support subtitle offset and the web player that does. Everything else is a version of the web player basically and they all support subtitle offset
Nvidia shield is a android device so it tracks that this is the mobile player without srt adjustment. That sucks though. Maybe I should look at kodi and jelly plugin…
If it uses he android client there should be a setting to choose which player, at least with mobilie there is.
On the client go to settings -> client settings -> video player
It might let you change it