There were deviations from the rules throughout the ages, especially on the left bank with the newer, taller towers (Place d'Italie, Montparnasse, Berges de Seine). But these deviations were always one off, pushed through by an ambitious leader that burned off a lot of political capital.
https://www.google.com/maps/@22.2816017,114.156159,3a,75y,31...
Some streets in Paris are narrow, others aren't. Streets with two-way road traffic are wide enough.
(OP is not talking about shadow on one side of the road. They mean perma shadow the whole day long.)
Rio de Janeiro is located at latitude 22.9 South while Paris is located at 48.8 North. The solar exposure of those cities throughout the year is very different.
The original post was about making taller buildings in paris without wider streets. That would lead to permanent canyons.
It's no wonder we're kind of vaccinated against towers... I could add to the list: place des fêtes, Olympiades, les Orgues de Flandres...
The canopy at Les Halles also pretty much puts a stop to the rumour that new, massive constructions are not possible in Paris, let alone in the center of Paris.
Granted, context certainly matters and Beaubourg was, charitably put, rather controversial when it was under construction, but it's absolutely not a given that no renewal is possible.
[1] https://en.wikipedia.org/wiki/Centre_Georges_Pompidou [2] https://www.citylab.com/design/2015/05/paris-the-canopy-fix/...
Keep in mind that Paris, without near suburbs ("proche banlieue") is only 105 km² and as written, has been mostly rebuild by Haussmann (following Napoleon III orders) in the late 18XX, when I.e. London is something like 1500 km² ... so comparison may be difficult