This might be true, but the world we live in where x86 is the open platform and ARM is a mess of incompatibility.
You want to install Ubuntu on your laptop? Download this ISO and you're good.
You want to install LineageOS on your phone? You have to download the exact binary for your phone (which means LineageOS needs to maintain those hundreds of versions) and hope your phone is supported.
The BIOS (or UEFI) is not used by most OSs which aren't DOS. The compatibility comes from the standard peripherals (DMA, PIT, PIC, FDC, 8042) and PnP interfaces like PCI (as well as standardised interfaces located behind them, e.g. USB OHCI/UHCI/EHCI/XHCI, SATA BMIDE, LPT, VGA, etc.)
The BIOS (or UEFI) provides a standard interface to load an operating system which can then discover which hardware is installed.
It's true that another factor is the software discoverability of hardware. A lot of stuff on ARM platforms is not discoverable because those platforms are intended to run specific software.
You want to install Ubuntu on your laptop? Download this ISO and you're good.
You want to install LineageOS on your phone? You have to download the exact binary for your phone (which means LineageOS needs to maintain those hundreds of versions) and hope your phone is supported.