We saw state and local election offices (and contractors they use) targeted by Russian intelligence services in the run up to the 2016 election. They compromised things like voter registration databases and software.
It would not surprise me one bit if Chinese intelligence was equally successful in 2020 (& 2024), or if Russia continued to enjoy access to these systems.
But remember, these aren't actual vote tabulators. These compromises can cause disruption, but can't easily alter votes.