You posted into a Windows OS forum, not Mac support forum
https://obsproject.com/forum/list/mac-support.33/ ??
most modern laptops no longer have a direct Ethernet port. However, via docking station or USB adapter, almost all of them can still use a wired Ethernet connection (vs WiFi)
All kinds of things can prevent a stable video stream being sent over WiFi... like many page, long detailed, fine print technical article. the simple workaround/test - don't use WiFi. Can WiFi work, especially in non-dense urban areas? yes, under the right conditions
That 80mbs I'm guessing is download speed... ie your ability to download videos, stream Netflix, etc.... has almost NOTHING to do with upload bandwidth for SENDING a live stream video
- if you say 'but I can watch Netflix [Amazon Prime/whatever] over the Internet.. I'll say 'yea, so what?' doesn't relate to
sending video, and you don't have the built-in cache/buffer that all those streaming tech systems use to over-come (and in doing so, mask from the unknowing masses) unstable Internet connections. And almost all of those consumer Internet connections are optimized for download, not upload
What is amazing that the really hard/demanding real-time video encoding for livestreaming works over the Internet (which when deployed to consumers was architected for an entirely different usage scenario, ie download no upload, and jitter a largely non-issue). Sometimes it works... and is amazing when it does. but in reality it is complex and technical. And when it goes wrong, troubleshooting isn't always easy.
As you are using WiFi, and can stream, but have unstable network throughput (bitrate), I'm guessing 90%+ that your house WiFi is the problem (nothing to do with OBS)