You're doing something after initialization, right?You're starting the BIOS from there, right?

Assume a PC (hardware called)

The CPU is connected to DRAM, ROM, etc. and can be executed from the specified address
At Power ON, the CPU starts running at a specific address (specific vector depending on the type of CPU, etc.).It has a hard ROM in it.
However, as soon as the power is turned on, you cannot use DRAM, let alone ROM and SRAM, so initialization is initialized

(About DRAM)
Static RAM is also used for CPU registers and caches, and is a combination of NOR gates of transistors.You can use it if the current is running.
Dynamic RAM uses a capacitor, and even if the current is running, it drains out and disappears, so you need to refresh the memory controller by rewriting the read.At startup, you must specify the timing to remember (DRAM Frequency)

Note:

• SRAMhttps://tinystones.net/mem/mem5.html
• DRAMhttps://tinystones.net/mem/mem3.html

"BIOS" has several meanings, and may have other meanings than the following

Basic input/outputs such as string output, string input, and disk I/O are called BIOS and are in ROM and can be called in service calls (past tense)
Recent ? The CPU is operating in 32-bit or 64-bit mode, so the 16-bit code does not work as it is.
The current form is to call the API (required) in the booted operating system.OS side should have all necessary APIs

Power-on self test (POST) such as whether the screen is on or the keyboard is connected should also be done by initializing the booted OS, so it would be twice as easy if it were done in ROM first.
The next generation boot to replace the BIOS ROM should be minimal (even now, self-checking a few GB of RAM takes time, so it should be omitted).
In UEFI, BIOS-POST is PrePre-EFI Initialization Module

Note:

• PDF documentation
• PDFDeveloping firmware for free PCs --yabits: Yet Another UEFI Implementation-
  • (ja.wikipedia.org)coreboot

• (ja.wikipedia.org)coreboot

(2) About the startup ROM
The startup ROM (firmware) often uses flash memory instead of mask ROM
This is a NOR flash memory, not a NAND (often used in SSDs, etc.) and can be addressed normally like a ROM (can be specified as a jump point for CPU, call instructions, etc.)
(Therefore, there is no need for steps such as reading from the CPU and transferring it to RAM.)

I don't know what I'd like to ask (or rather at all), but it's no use trying to figure out how you view the word "initialization" if you and your readers don't agree.

Each piece of hardware

It's the various elements that make up a PC.For example, DIMMs, PCI-e cards, keyboards, etc.

If the DIMM is not inserted, or if the power is turned on with incomplete insertion and poor contact, the main memory is not present from the PC perspective of the PC.Alternatively, the DIMM may be defective/overclocked and the CPU may not respond correctly to the read/write operation.

Alternatively, replacing parts may change or extinguish the large storage device that needs to boot to the operating system.

You don't have to initialize the memory controller, PCI, FPU, graphics, etc. in the BIOS, do you?

Various parts (boards) will respond to a given signal = Self-initialization of the board is a prerequisite (Oira imagines this is the initialization of the questioner), but it is not enough to initialize a PC.

Before the operating system started, it was common for PCs to have multiple displays, and users would be troubled if they did not identify which display and at what resolution the POST screen should be displayed at the BIOS level, check display priority, etc.