How can I view the typical flight prices (ideally during a given date of the year) between two airports prior to the COVID-19 pandemic? Google Flights only show the future prices.
The closest thing to a useful answer is here. ExpertFlyer is a subscription service that can show historical fares up to a year ago. This is not enough to go back before COVID-19 now, but it was at the time Franck Dernoncourt's question here was posted.
The historical fares don't necessarily indicate prices at which flights could actually be purchased, because (particularly on the highly discounted end) they could be fares for which the airline did not release any seats at a given time. But they are of some use as a guide.
Also it's important to note that airfares depend on two dates, the flight date and the purchase date. The effect of COVID-19 (or any other unforeseen event) on airfares would be most directly associated with the purchase date. That is, fares quoted before March 2020 for travel after March 2020 would still be "normal".
Not really an answer but too long for a comment:
Even before Covid there was no such thing as "typical" prices. I've flown US east coast to China for as little as $400 and also for over $2000: Same plane, same seats. I've flown business class to LA since it was cheaper than economy (on the same flight). Even budget carriers like Ryan Air will vary the prices by factor of three or more from one day to the next depending on how full the planes are. We flew a multi city itinerary and a single small tweak at one routing reduced the price for the total thing by a factor of 5.
In order to answer the question, you would need an operational definition of "typical".