Linux users who have Secure Boot enabled on their systems knowingly or unknowingly rely on a key from Microsoft that is set to expire in September. After that point, Microsoft will no longer use that key to sign the shim first-stage UEFI bootloader that is used by Linux distributions to boot the kernel with Secure Boot. But the replacement key, which has been available since 2023, may not be installed on many systems; worse yet, it may require the hardware vendor to issue an update for the system firmware, which may or may not happen. It seems that the vast majority of systems will not be lost in the shuffle, but it may require extra work from distributors and users.
I wish all the firmware for every motherboard was made public and open sourced. Even if a company has proprietary firmware/drivers, I would hope that once that product reaches end of life that they do in fact open source that code so that someone else can pick up where they left off.
I 100% agree that they should not brick their hardware once it reaches end of life. There might be someone out there who would take on the task of maintaining it, which is better than nobody maintaining it.