Thx for the reply zpm1066… 
Yes a power cycle is the need to bring it back, then blinking the LED from the hex code uploaded from first successful attempt…
I also tried the the hex file compiled by Arudino IDE 2.0b6, had the same effect. Tried scratching on the Net for a bare metal blink hex file by Raspberry Pi Pico SDK, no luck… I wanted to eliminate MBedOS as a possible cause…
Your test was it with a Pi Pico, or a Tiny2040 as shown in your github post?