Heading out for CONFERENCE in Las Vegas and thinking of staying over afterwards five days is it worth E Biking in Las Vegas or going to other areas e.g. Moab?
Also, any advice of what else are doing? Las Vegas? I understand it’s very hot we are going in June.
For a guy coming from England, you are in for a whole new range of temperature.

Vegas can get to ungodly temperatures. Do not underestimate how baren and hot it can get, though June can also be mild enough. Looks like someone local to the area gave some recommendations. I personally have not ridden there, I usually just go for food & booze.
I'll second a trip to Zion National Park. The hike to Angels Landing is absolutely incredible, in June, start as early as you can, then get down off the mountain, have lunch & hike "The Narrows". You will need water shoes and a hiking stick. You can do both in 1 day if time limited, my wife and I did it in our 40's. I'd still do it in my 50's.
Also, in the Las Vegas area, if you have not been to Hoover Dam, that is a cool tour. You would want to plan it and get good tour tickets, you can go down into the Dam, see the power house, etc. The Vegas buskers will try to sell you a trip, but you can book directly online and just drive there.
E-bikes are not as accepted in the US, as they are in Europe, so many trails can be off limits. Some people ignore it, and being not from here... You can just play dumb... I do it all the time. Just not in a place like Sedona, those guys ticket you.
If you have not been to the California coast, you can go to a place like Santa Cruz and rent & ride the local places, like Wilder Ranch. Just watch out for poison oak. Not sure if you guys have anything like that, but my rule is, don't touch anything. If you end up wanting to go there, ping me, I'm 2 Hrs away & will head over for the day if I can.
Have a great trip over, the West of the US is so expansive and there is a lot of nothing between cool places. Not sure if you have been before, but no matter how many times you come, there is something new to see.