It does take too long to enter a keyword! First, some things you may have already done: Go to an album with your Grand Canyon trip, select them all, open the info window (command-i) and enter the keyword "Grand Canyon" for all of them at once. Do that with anything an album will help with. Also you can use search, or smart albums to help gather all the pictures with "boat" in them, for instance, and do the same mass keywording. This works great for some set of the keywords you may want to use. And you can use the face ID to choose a person, and add a keyword for most of their pictures.
But you can use the Keywords Manager to make it easier for the hard ones. Use command-k to open the manager, and choose Edit Keywords. Scroll down to a keyword you want to use a lot, maybe "Mustang" if you like cars, select it, go to the right side of that line and click, and it should open a little blank for you to enter a "Shortcut," maybe "m". Close by hitting OK, and at the top you will see "Mustang" with a little "m" next to it. Keep the Keyword Manager open, but you can move it out of the way. (I leave a tiny bit of the upper-left corner visible in the lower right corner of the screen.)
Now, with the manager open and out of the way, whenever you have a picture selected, you just type m, and you'll see "Mustang" appear for a moment in the picture, and "Mustang" will be added to the picture's keyword list. You can set it up with "c" as a shortcut for "coolcar" so you can type "c" on the same picture and add that. The thing is, this is pretty fast. And you just type "mc" and get it done all at once. If you can remember the shortcuts, you can add bunches to a picture each time. And you can select several pictures and use shortcuts on all of them at once.
By the way, typing "m" when "Mustang" is already a keyword removes that keyword.
I think all this is here:
Find photos by keyword in Photos on Mac - Apple Support
