Hello - Android stopped allowing 3rd party access to WiFi Hotspot a few OS's ago which really pissed me off because like you I used Tasker to turn on Wifi hotspot everytime my phone connected to my car's bluetooth.
The only way to do it (without root) on newer versions of Android is to use the AutoInput plugin to emulate turning on your phone and pressing the right buttons to turn it on. This is not 100% successful as it can depend on many factors such as if your phone is in your pocket when it turns on, the screen may possibly detect other touches than the autoinput ones. And even when docked, for whatever reason, sometimes the AutoInput action doesn't work, but overall I've gotten about 80% success rate.
There's a thread somewhere on here that explains how to check if the hotspot is on so I added a task to test if it's on after the autoinput action and if it's not on, I then try again.
It's a pain and not nearly as good as just being able to have Tasker turn it on, but that's Android's fault for locking it down. Nothing Tasker can so about that...
On a side note, as much as I get annoyed by Bixby, the one thing Bixby is good at is changing settings by voice so when I say "Hi Bixby, Turn on Mobile Hotspot" Bixby is able to do it with no problem.