Quite a few candidates if:
https://en.wikipedia.org/wiki/List_of_heads_of_regimes_who_were_later_imprisoned
... [sort by country] is anything to go by...
Andalusia (technically an autonomous community in Spain) appears to have two former presidents sitting in jail since 2016.
Argentina has a whopping 8 presidents that sat in jail, including 2 from 2007 onward.
Bangladesh had 5 presidents who went to jail, of which two were behind bars in 1975.
Bosnia and Herzegovina had 2 presidents sitting in jail from 2006 to 2012.
Bulgaria had as many as 3 former prime ministers behind bars at the same time in 1944.
Comoros has 3 presidents and prime ministers behind bars at the time of writing this.
Costa Rica had 2 presidents behind bars from 2004 to 2012.
I'll stop at C, since the list is long, with a few honorable mentions:
Egypt appears to have had 5 former presidents in jail in 2013.
Guatemala 3 early in 2018
Hungary 4 in 1945
Iraq 4 in 2004
Japan 5 in 1945
Libya 4 in 2011
Pakistan 4 + 2 arrest warrants as I write this
The point is Brazil is not an exception.
One caveat: read the list with a fistful of salt, because it lists former French President Sarkozy as sitting behind bars since 2018, whereas he was only put in police custody for a day that year as he was charged with bribery and illegal campaign contributions. (He might sit in jail some day in the future, but the point here is that you may want to double check the data.) Also, Gaston Flosse of French Polynesia is listed twice.