The answer: Electron. Always.
What is also baffling is that a multi-billion dollar company with hundreds of employees is unable to create a cross-platform native desktop app, yet it takes ONE PERSON [0] to create a desktop client for Slack and Discord. The fact that Slack is already 'optimising' Electron via offloading / rewriting JS code in C++ / Rust tells me that JS will never give them the performance requirements they need.
For Slack there are no more excuses to try the Qt option.