Add support for Brazilian Real (BRL) as a formatting option in Proton Sheets, under the menu 'Format > Number > More Currency'. The name, following the pattern, would be 'R$ Brazilian Real'.

Related requests:
https://protonmail.uservoice.com/forums/932839-proton-drive/suggestions/50774645-proton-sheets-support-for-swiss-francs-in-curren
https://protonmail.uservoice.com/forums/932839-proton-drive/suggestions/50787686-proton-sheets-support-for-czech-currency-k%C4%8D-c