Help with Ginseng Ficus!

[CS0719]

Hi! I’ve had this focus for over a year. I took it to a garden place to get it repotted and since then, it has begun to worsen. The person who repotted it placed it in this pot but with compact houseplant soil. I, who know nothing about plants, thought it was perfect. But after doing research, I bought this “bonsai specific” potting mix and changed it over a week ago. While changing it, i noticed the trunk was so squishy and i’m afraid it has trunk rot. In order to remove the old compact soil, i used some water and so i haven’t watered it since then. it’s been about 5-7 days since changing the potting mix and i don’t know what to do.
Also, the plant sits in this window ledge and only used to get watered when the soil was dry so every 10-ish days. You can see the bottom rig by trunk portion looks indented, it’s because it is. That’s where it’s squishy. Please help.

 

[CS0719]

Also, 3 weeks ago there were new leaves growing and they fell off a week ago.

 

[Jester217300]

This one has unfortunately passed on.

 

[Shibui]

Bonsai can grow in any type of soil. The open bonsai type soil is only so we can get away with overwatering because most of us do.

The squishy trunk indicates you have kept the soil waterlogged, probably well before either repot but only you can know how it was cared for back then.
Constantly wet soil encourages root rotting fungal infections. Ficus can look Ok for months despite having rotted roots so we often don't pick up the signs until way too late.
Ficus are one of the toughest trees going but, this time, I'll agree with Jester. It's too late for this ficus.

Wash and disinfect the pot and keep it for your next try.
I note the pot is sitting on a bench but no tray under. Does the pot have a drain hole? No drain hole is a sure recipe for disaster with any plants.