A hood definitely would help, though it might not completely reduce the problem.
The correct, bayonet mount hood comes with the lens (according to Fuji USA and Fuji Global websites, as well as B&H and other retailers who list "what comes in the box").
If you've lost yours, replacements are available, but aren't easy to find! There's no "model number" for it given anywhere I can find.
But I did find:
https://www.keh.com/shop/fuji-x-series-18-135-xf-18-135-f-3-5-5-6-r-lm-ois-wr.htmlBe sure to get the correct,
bayonet mount type hood. The wrong hood can cause vignetting (partial blocking of the image in the corners, especially at wide angle zoom settings).
There are cheaper "generic/fake" hoods that are all too easily mis-positioned so that they cause vignetting. This is an example...
https://www.walmart.com/ip/Fujifilm-XF-18-135mm-f-3-5-5-6-R-LM-OIS-WR-Pro-Digital-Lens-Hood-Flower-Design-67mm-Nw-Direct-Microfiber-Cleaning-Cloth/421835305?wmlspartner=wlpa&selectedSellerId=2781&adid=22222222227097607666&wl0=&wl1=g&wl2=c&wl3=234327692574&wl4=pla-387649612475&wl5=9032191&wl6=&wl7=&wl8=&wl9=pla&wl10=117079859&wl11=online&wl12=421835305&wl13=&veh=sem&gclid=Cj0KCQjwr4beBRDNARIsAGZaZ5f5VVm0vRG860bNdpEHRIzOGfVLo1ueAtoe2o0D1VF_-I-zCLo_F5waAi1-EALw_wcBBy "fake" I mean that these aren't true bayonet mount hoods. They screw in, then you need to rotate them to align them (and they are easily bumped out of alignment). And often they are a "one size fits all" that either doesn't shade the lens very well or causes vignetting. You'll find lots of those fake hoods on eBay, Amazon and elsewhere. If at all possible, I'd recommend getting a genuine bayonet mount (contact Fuji directly, if need be). I would only resort to one of the generic/fake hoods as a last resort (it's better than nothing).
ALSO... do you have a "protection" filter on your lens? If so, that might be amplifying that flare. Try some test shots without it. Besides, once you have the proper lens hood, that will do a good job physically protecting the lens from many things... better than some thin piece of glass ever could.
If you MUST use a filter (any filter for any reason)... be sure it's high quality and
multi-coated to reduce the risk of problems with flare.
A hood definitely would help, though it might not ... (