Initially, Bootcamp for Intel Macs consisted of three things:

1. a BIOS compatibility support module (CSM) for Apple's EFI firmware, allowing legacy bootloaders and option ROMs to be used. (Macs released after the first version of Bootcamp came with a CSM out of the box, while earlier Intel Macs needed a firmware update to provide the CSM.)

2. a collection of Windows drivers for the peripherals shipped in Intel Macs

3. a graphical tool to assist with the process of installing Windows (partitioning, etc.)

Linux never needed (2), and (3) was always more of a convenience than a necessity. The need for (1) lessened over the years as both Linux and Windows gained full support for booting from UEFI without a BIOS CSM, and as Apple's firmware evolved to more closely resemble UEFI 2.x than EFI 1.10.

I don’t think bootcamp has ever been a requirement to boot into linux on a mac, and I never have used it to do so on various macbook pros over the last ~10 years