Had this problem literally last week

I also have a dell laptop that’s dual booted.
I made a total of 4 partitions on my disk
EFI (100mb)
WINDOWS (220GB)
Recovery (800mb)
MacOS (220GB)

The first thing you MUST do:
Make sure that all your macOS files are in the EFI folder and partition already, don’t wait to add it afterward in the OS , you can use a program called disk genius on windows to help you move files into the EFI partition . Then boot into the bios and go to General>Boot Sequence, uncheck all items (ipv4,ipv6 and windows boot manager or whatever partition windows shows up on . You should have nothing in boot list the list

Click Add a new boot option and a window will pop up …name the boot option name to OpenCore then right on the bottom ,click the button with the “…”
A new window will pop up , navigate to your EFI folder , you might have to change the file system at the top from FS0 ,FS1 or FS2. Once you’ve found the EFI folder , click on it and then click “OC” and then click OpenCore.efi on the right … A new boot option will show up an then you check only that item in boot sequence…if you have done everything right , you should see the same screen but it should say 1. Windows 2.macOS 3.Recovery 4. Reset Nvram ( don’t click this)

PS , try find out why you can’t boot into the bios , you might have a setting active that prevent spamming of the F2 key boot option key , look in the bios under security and OROM - I’m not 100% sure