You don't. You could stay on an old MacOS. Apple would prefer that you tell your customers to stop being poor and buy a new computer. They will make your situation increasingly unbearable until you do.
The overwhelming majority of people haven't needed a new computer since 2016. The current economic situation makes a new computer a worse value proposition than it's been in 35 years. Vendors are responding to this situation by manufacturing obsolescence. Microsoft pulled the same stunt with Windows 11's TPM 2.0 requirement.