Best way to get 20 amps to outdoor office 150' from breaker box
Run 2-2-2-4 MH feeder from the panel to the office.
The reason is the distance and very severe voltage drop on 120V circuits.  Normally I'm pretty slack about voltage drop.  However 200' at 120V is so bad even I have to stand up and take notice.
And it isn't even a case of 1 wire size bump (to 10/2)... that might work at 100' but at 200', just off the cuff I can tell you that you'll need a second bump to 8/2.
And now we get into a costing problem.  8/2 UF-B is $1.28/foot.   Well, heck.  2-2-2-4 MH feeder is $1.27/foot.  Why are we putting in 40A/120V cable when we can put in 90A/240V cable for less money?  It simply doesn't make any sense!
Of course you can't land #2Al wire on a 120V receptacle (can't land #8 either)... so the cheapest solution for landing #2 on a recep is just running a subpanel.

Use a 60A feed breaker (the wire is good for 90A but 60A is the cheapest breaker that'll take #2 wire).
The subpanel needs a disconnect switch (being an outbuilding).  I would select a 12-space or larger subpanel that is convertible to main-breaker (don't convert it yet).
I would simply connect the feeder wires to the subpanel's main lugs and install ONE 20A/240V breaker ($10).  That will serve as the main disconnect since it is the only breaker.  You can power up to two 120V/20A circuits off of that.
Voltage drop will simply be a non-factor for a 120V/20A load.
Later on, if you want to grow that into a real subpanel, you simply retrofit the main breaker and install as many breakers as you please.
At 200', voltage drop at 240V isn't a big deal.  You're allowed to plan to use up to 72A on that circuit, and at 72A you'll have 3.52% voltage drop.  That's no big deal.
So yeah, if you want to install seven 2000W Cadet heaters to make the building warm up real fast, go for it.