Yes, both the M1 iPad and M1 Macbook Air have Bluetooth 5.0 listed on the spec sheet.Do your ipad and mac use the same bluetooth version?
The antennas are also completely different - the mac may actually be more sensitive to interference since it's a larger footprint.
Indeed the antenna and body designs are completely different and that probably has a lot to do with it, but considering that Apple mainly sells bluetooth accessories (Magic Mouse/Keyboard, AirPods/Beats), the MacBooks should at least be able to run a bluetooth mouse, keyboard and headphones simultaneously without issues. The iPad can do it after all. And if they can’t, that limitation should be clearly tested and stated.
Bluetooth 5.0 spec states that it supports 7 connections at once, so you’d expect at least 3 connections to work flawlessly, especially when it’s a premium device and when another device from the same generation can do it.