Start with getting the battery load tested. Alternatively, pay attention to voltage reading on dash while cranking. If it drops to around 8-10V, you don't have enough voltage to run electronics while cranking.
If the voltage looks ok...steady around 10V and above, maybe with a jump start on the battery, then look at rpm reading on dash while cranking. If you have 0rpm reading, your crank angle sensor is faulty(providing you have enough battery voltage so always better to start with a load test).

 

Thank you MoHawk for your response. I couldn’t get the battery load tested yet, however is an almost new YUASA installed by the KTM dealer 5 months ago.
I looked at the voltage reading when cranking - is a constant 10.6V (dropping from 12.6V)
Checked the RPM reading when cranking – zero.

 

Looks like you have a faulty crank angle sensor. If you are taking it to a dealer, a scan should confirm it. Otherwise fit one yourself. I believe KTM calls it an "impulse" or "spark" generator.
No. 13....$71.39

2020 KTM 790 DUKE Ignition System | KTM World

Shop online for OEM Ignition System parts that fit your 2020 KTM 790 DUKE, search all our OEM Parts or call at 770-748-0771

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Thank you! I need to look & see how easy is to replace it. From the diagram looks like is on the outside/side of the engine

 

Can't be sure(not near my bike) but I believe the left side cover needs to come off. Carefull with the bolts. Remove slowly by hand. Hopefully somebody that has done it before will chime in.
Make sure everything else looks normal first. Like when you put ignition on(before cranking), listen that fuel pump primes and dash looks normal(with neutral light). Checking all fuses wont hurt either(easy with a test light). Trying to rule out if your BT fried something that effects that sensor.
You can also test that sensor to confirm, but that gets a bit more difficult to explain.

 

Thanks a lot MoHawk