Brazil has electronic voting since 1996, and despite not being perfect, I think the system works well enough. It's offline, runs its own Linux-based OS, and runs open source software digitally signed by the electoral court.

Official government site for it: https://international.tse.jus.br/en/electronic-ballot-box/pr...

Recent video about the electronic voting system: https://youtu.be/glktxz5tIQ4?is=U0Sujv0n3NUxgV9N [in Portuguese, but English subtitles available]