Welcome and Thank you too :-))
Well that is an option but certainly there is another option without the purchase of new equipment.
It would involve pretty much removing almost everything from the machine thereby making space for the Big Sur to download. Not Installing but creating a Bootable Installer of Big Sur. Now, need confirmation this is the machine you want to install Big Sur onto - MacBook Air 11″, macOS 10.15.
Understand - the next possible instructions will involve Booting from the Bootable Installer of Big Sur and then Wiping the Entire Internal Drive of everything. Nothing will remain and no do overs.
Should you wish to explore this avenue - please advise and will provided detailed instructions - step by step.
Further notation - the machine has at least 8 GB RAM otherwise the experience in Big Sur will not great versus the effort to install it.