Since you can see the headphone icon in Android, I assume that the tablet thinks that you have headphones connected.
It may be a broken headphone jack or perhaps the jack is dirty.
Try to blow hard into the headphone jack, plug in and plug out headphones a few times…
If nothing works, I guess the headphone jack is broken. I don’t know if it’s hard to change on the X98 Plus, I haven’t even been able to open mine.
There is always the chance that it’s a software problem, but it feels like it wouldn’t be in both operating systems in that case.