Hey @tech-netharmonix,
I’m the Multipass Engineering Manager and @xnox made me aware of your issue here. I’ll explain why you are seeing this.
I assume you have an Intel Mac and as such, hyperkit is the default driver at this time. The way Hyperkit works is that it boots the kernel directly via grub, so when you update the kernel inside the instance, it won’t boot the newer kernel since the kernel that is booted lives outside the instance. This is just a limitation of Hyperkit unfortunately.
That said, we now support qemu on macOS 10.15 and greater and this is a much better solution for macOS. QEMU boots via UEFI, so no need for booting the kernel directly and thus, kernel upgrades in the instance will work.
You can switch to the qemu driver via $ multipass set local.driver=qemu. There is one big caveat to this though- switching to qemu will make any existing hyperkit instances unavailable, but not deleted. We will soon be working on a way to seemlessly update hyperkit instances to qemu instances and make qemu default on macOS, but we aren’t there yet 
If you have any other Multipass related issues/questions, please feel free to open a new issue at https://github.com/canonical/multipass/issues/ or post to Multipass - Ubuntu Community Hub .
Thanks!