I'm no expert in how economists use the term, but I suppose it could certainly be called a shortage if there is some systemic reason why restaurants can't (or at least think they can't) raise prices in the short term. Personally I don't find that likely, at least based in my region where restaurants have indeed raised prices and many seem to be thriving (although many others failed in 2020).
In a normal economy, most restaurants fail for two simple reasons; poor location and undercapitalization. If you sell a good meal, in a good location, people are very tolerant of price. Getting to that point is where 99% of restaurants fail.
