How long will apple provide support for MacBook Air 2020 with M1 chip?

Unknown. Apple does to disclose life spans of products. Though generally macOS upgrade support has been known to last around 5 to 7 years from release. At which point its dropped from major OS upgrades and only provided security updates for the last available macOS version for it for a couple more years.

This however was applicable with Intel Macs. Apple silicon Macs have yet to reach end of support, so it's impossible to know when they might, and whether or not they will keep with this time frame.

In addition to Phil0124 excellent replies, you may find these articles handy:

• Obtaining service for your Apple product after an expired warranty - Apple Support
• What It Means When Your Apple Products Become 'Vintage' or 'Obsolete' - lifehacker

1. There is no YouTube app for Mac. You would use the website directly. The iPad Youtube App is not available for download on Macs. You likely find this to be the case for many iPad Apps.
2. All devices including Macs will eventually stop being supported and eventually an M1 MacBook Air would also be unable to access the Youtube website, but that's going to take longer than on an iPad. App Support usually continues for many years on Macs past when Apple stops providing OS upgrades though.
3. A MacBook Air and an iPad are very very different devices. And run very different OSes.

You're welcome.