Not the OP but JP Morgan’s Kapital system which underpins their credit hybrids business was smalltalk.

I say was because i believe it’s been deco’d in the past few years but i don’t know for sure, when i worked at JP it was still a core breadwinning system.

They have an extensive list at https://pharo.org/success/.

I believe the core of Gemstone is smalltalk - it's an object database/runtime and supports java as well - they also sponsored/made maglev ruby (now dead?):

https://gemtalksystems.com/about/customers/

Most of them were financial industries, and a gov body in charge of tax processing and that stuff.