Discount stores measure bikes by wheel or tire size. WRONG! Adult sized bikes from a REAL bicycle shop will be measured by frame size. If you're 6' 1" tall looking for a hybrid/city bike, I can just about guarantee they'll all have 700 X something size tires...700 X 32c - 700 X 35c - 700 X 38c, etc.
Know how to choose the correct size bike? In all capital letters...QUIT LOOKING ONLINE! Go to a REAL bicycle shop & TEST RIDE as many as you want and/or can. You may have to leave collateral, such as a drivers license or credit card - but TEST RIDES ARE FREE!
Why are test rides so vitally important? Because frame sizing from one company to the next is NOT universal. An XL (or 21" frame) from company 'A' might be measured different by company 'B'. Some measure from the center of the crank all the way up to the very top of the seat-post tube. Some measure from the center of the crank to the INTERSECTION where the seat-post tube joins the top tube. That could be an inch or more difference. Read all about frame sizing from the late cycling Guru, Sheldon Brown on this link... https://www.sheldonbrown.com/frame-sizing.html
If you're thinking about buying online...here's one word of advice. DON'T! A) What guarantee do you have there won't be hidden damage inside the box? NONE. B) Who assembles & tunes-up the bike? YOU! Or you pay a bike shop mechanic to do it right. Oooops...there went all your online savings. C) You read correctly...tune-up the bike. They all come out of the box needing at least minor adjustments. D) Buying online, what sort of after-the-sale "Service Warranty" do you have? NONE! All bikes from a REAL bike shop come with a service warranty good for at least one FREE tune-up as the bike gets settled in. Spoke tension on the wheels might need to be adjusted. Or, shift & brake cable tension might need to be tweaked.
If you truly want to "make sure" you get "the right size of hybrid/city bike" - follow these five, simple-to-understand words... Go To A Bicycle Shop. The $$$ stays in a local community business. You'll get a MUCH better product. You'll get a local warranty!