There is no one, universal key press to kick you into boot options of UEFI/BIOS across brands of computer and brands of UEFI/BIOS.

On HP machines, it's Escape during a cold boot.  On Dells I believe it is F12.  There are some that use F2.  Way back when, F8 was often used to invoke Safe Mode, but it wouldn't surprise me if some machine may have used it to trigger BIOS.

You have to determine how one gets into BIOS for a given machine.  Also, if you are doing a first-time install of an operating system on a machine that's never had one, or a completely clean reinstall of Windows, you do have to get into UEFI/BIOS to do so and there is no screen reader support at that level, and in all probability never will be.  By contrast, a Repair Install or Feature Update can be triggered from within an existing running Windows instance and will be accessible using Narrator once the process gets far enough along to allow it to be invoked, and that's pretty early on.  You generally have a very short period of time where all of the initial work is being done where Narrator will not start with CTRL + WinKey + Enter, but if you keep trying it eventually will come up.
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Brian - Windows 10, 64-Bit, Version 21H1, Build 19043

The stoical scheme of supplying our wants by lopping off our desires is like cutting off our feet when we want shoes.

         ~ Jonathan Swift (1667-1745)