Depends on your fitness, it's certainly going to be harder work (not exactly a shock). Gearing is not such a big deal if you can spin unless they're pushing it. But if they are then you're not going to keep up anyway unless you're a level above them. You certainly don't need to faff around with anything like aero bars!
Bear in mind there's a lot of stretching the truth/flat out lying on the internet about the speed roadies go. If you believe people no-one averages less than 20, the reality is more like 15 according to strava end of year reports. Of course some do but it's rare. But even at 20 you won't run out of gears very often if at all (perhaps with a 1x with tiny chainring).
Totally agree with this. 15mph avg is a very good road pace for solo, fit, normal riders, having a training ride, on road bikes, gravel bikes or mtbs as long as the latter have decent tyres and bars that aren't meters wide. Decent tyres can be 26" slicks, semi-slicks or even fast rolling knobbed tyres, like conti race kings.
A group ride of normally fit people can be a bit quicker but only nudges a twenty average with more of a 'chaingang' club ride, ime, with some road hardcore doing the pulling. Old school mtb gearing had the top gears to manage, but some of the ultra modern 1x top gears will see you spinning like mad, in some situations. At the end of the day it is fitness that counts. Super fit mtb riders will kick the arse of normal fit road riders.
Many, many moons ago i was more roadie and raced time trials and track. On one time trial a top rider finished on a ladies step through shopper and still wasn't much over an hour, for 25 miles. He had punctured, or something, after having just overtaken the lady shopper. He pulled over and after a bit of quick thinking stopped the lady and asked if he could take her bike, to the finish. A deal was struck so she wheeled the stricken lo-pro, to the shops, and he did the last 5 miles on her shopper, in his lycra and aero helmet but no shoes as they were slipping on the pedals and he had stopped, removed them, and put them in his skinsuit. A good example of how determination and some adrenaline can get you through.
Personally; I have always found not having enough to eat and drink and/or being cold have been more of an anchor than anything else. 100-200 miles can be a joy on road bike or mtb, as long as it fits well, but 20-50 miles can be absolute misery, both physically and psychologically, without food and water or if you are cold even with effort.