I will never travel to Europe in June/July/August, even without Covid. It's the heat!
In 2017, we did a long road trip through Western Europe, from early May to late June. Got caught in a heat wave at the end, and were miserable.
In 2019, started out earlier in April, and ended in May. Much, much better.
In the past we have done a couple of impromptu late fall trips when seeing fares so low we could not resist. Not good moves. It was not that cold in November, but the days were so short, and many tourist attractions closed for the season. I still remember wandering the streets of Kutna Hora, looking for the train station to get us back to Prague. In the rain, and at 4PM, it was dark, and the streets were deserted. There was no Google Map back then.
Anyway, I will do April/May, and September/October from now on. May even try March/April. Did February one time, and it was not bad at all in Southern France and Southern Italy.
The only problem is Scandinavian countries where it's cold like heck, except in the summer.