In the past, several SSD manufacturers had bugs in their firmwares. So to be sure that I can fix such issues with a newly bought SSD, I need some secure (and somewhat easy) way of updating the firmware.
I don’t need to do the update on my own Linux installation. A bootable ISO would be fine, too.
Which manufacturer has some well supported way of updating SSD firmware, even if I don’t have any Windows installations left?
Assuming you’re talking about the firmware on the device and not the firmware distributed with the kernel/distro to interface with the hardware, I would identify a vendor that uploads to the Linux Vendor Firmware Service for their SSDs.