How important is Youtube audio quality

You might have come across those Youtube tutorial videos with either -Text instead of voice, -Computer generated robot-voice, or just low sound. Each of these are just not nice to watch and will cause a high bounce rate on your YouTube videos. A higher bounce rate might give your video a low quality score and less recommendations by YouTube. To create tutorials or gameplay videos you don't need an expensive hardware microphone. A simple headphone will work if you know what you're doing.

Why human speech?

People are lazy and generally don't want to see in front of their screen to watch you type instructions. They want that human element of another human telling them what to do. A human voice is more trustable than text on a screen. Let me give an example. If you're making a tutorial about how to download and use a free software.. you actually telling someone gives them more trust than an unknown person that is hiding behind text. That's just how it is. In human speech there is emotion and character. People are emotional beings and like to hear emotion from another person as well.
It is definitely not recommended to use computer generated robot voice. Besides YouTube's algorithm potentially not recommending your video (for low quality), the viewers won't like it either. The YouTube algorithm is there to keep the user retention high and keep the eyes as may hours as possible attached to it. More user-time is more money so your video will be valued if you can keep the user's attention. A robot voice won't help with that for sure.
But wait, I remember those old tutorials with screen recorders and text written in realtime in notepad. Text used to work right? Yes, things have changed. If someone wants text, they will use Google and read it on a website. On YouTube, people expect to see a video and hear sound. You don't want people to get annoyed. You're here to build an audience and get as many views (or downloads) as possible. Human voice is almost a must for that. This will only work if you speak properly English though.

Noice cancelling

A huge issue is high background noices. Whether you're sitting somewhere outside, or have a loud dog, or kids are playing around, you don't want their background noices in your video. This lowers the video quality and makes it less pleasant to listen to.
The big question is. Do I need a $100 microphone? The answer is no. Especially not for a beginner doing gaming videos or other tutorials. The technology nowadays is good enough that a simple headphone has a good enough microphone and that additional software is enough to boost the quality to almost professional levels. There is free noice cancelling solutions out there that make the sound crisp and clear in realtime. Usually the video editing software also has plugins or free options to edit the audio.