Qualcomm provides 8 years of support from platform launch. OEMs/ODMs need to choose to pay for it. Fairphone doesn't ship proper updates from the beginning due to lagging months behind on incomplete backports and years behind on complete updates.
It's entirely possible to port to a new kernel LTS branch regardless of what the SoC vendor provides, but they don't either way. Fairphone 5 and earlier have an end-of-life Linux kernel branch without security support. The Linux kernel is an immensely important part of security on a device against both local, proximity and fully remote attacks. Not having security support for the kernel means the device lacks real ongoing security support.
Android 15 does not receive most privacy/security patches but rather backports of many High and Critical severity patches. Only the latest OS releases receive Low and Moderate severity patches. A growing number of High and Critical severity patches are no longer backported due to how many vulnerabilities are now being discovered.
It's entirely possible to port to a new kernel LTS branch regardless of what the SoC vendor provides, but they don't either way. Fairphone 5 and earlier have an end-of-life Linux kernel branch without security support. The Linux kernel is an immensely important part of security on a device against both local, proximity and fully remote attacks. Not having security support for the kernel means the device lacks real ongoing security support.
Android 15 does not receive most privacy/security patches but rather backports of many High and Critical severity patches. Only the latest OS releases receive Low and Moderate severity patches. A growing number of High and Critical severity patches are no longer backported due to how many vulnerabilities are now being discovered.