You could try experimenting with Hydraulic Conveyor [1]. I built it originally due to the frustrations involved in distributing P2P software during my old Bitcoin days so you won't get any hate from me about that ;)

Conveyor can package Electron apps and also do all the Mac specific stuff from any platform including Linux. So it can sign, notarize and staple the app itself, also bundling Sparkle updates as it goes. We're listed on the Electron website these days. You may have more luck with it. There's a Discord channel for help too if you get stuck.

[1] https://hydraulic.dev/ (disclosure: my company)