According to the DEPRECATION section of the apt-key man page:

Except for using apt-key del in maintainer scripts, the use of apt-key is deprecated. This section shows how to replace existing use of apt-key.

The man page contains some hints and an example how to convert command snippets with apt-key to a supported command.

Deprecated:

wget -qO- https://myrepo.example/myrepo.asc | sudo apt-key add -

Supported replacement:

wget -qO- https://myrepo.example/myrepo.asc | sudo tee /etc/apt/trusted.gpg.d/myrepo.asc

Recommended replacement:

wget -qO- https://myrepo.example/myrepo.asc | sudo tee /etc/apt/keyrings/myrepo.asc
deb [signed-by=/etc/apt/keyrings/myrepo.asc arch=amd64] https://myrepo.example/debian main

Example with raspberrypi.org repositories:

root@raspi1:~# apt update
Hit:1 http://raspbian.raspberrypi.org/raspbian bookworm InRelease
Hit:2 http://archive.raspberrypi.org/debian bookworm InRelease
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
All packages are up to date.
W: http://raspbian.raspberrypi.org/raspbian/dists/bookworm/InRelease: Key is stored in legacy trusted.gpg keyring (/etc/apt/trusted.gpg), see the DEPRECATION section in apt-key(8) for details.
W: http://archive.raspberrypi.org/debian/dists/bookworm/InRelease: Key is stored in legacy trusted.gpg keyring (/etc/apt/trusted.gpg), see the DEPRECATION section in apt-key(8) for details.
root@raspi1:~# wget -qO- http://raspbian.raspberrypi.org/raspbian.public.key | sudo tee /etc/apt/trusted.gpg.d/raspbian-raspberrypi.asc
root@raspi1:~# wget -qO- http://archive.raspberrypi.org/debian/raspberrypi.gpg.key | sudo tee /etc/apt/trusted.gpg.d/archive-raspberrypi.asc
root@raspi1:~# apt update
Hit:1 http://raspbian.raspberrypi.org/raspbian bookworm InRelease
Hit:2 http://archive.raspberrypi.org/debian bookworm InRelease
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
All packages are up to date.
root@raspi1:~# 

To download all deb packages, perform an upgrade, dist-upgrade or full-upgrade with the –download-only parameter.

apt-get full-upgrade --download-only

Example

root@server:~# apt-get full-upgrade --download-only
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
Calculating upgrade... Done
The following packages will be upgraded:
  openssh-server 
1 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
Need to get 456 kB/456 kB of archives.
After this operation, 512 kB of additional disk space will be used.
Do you want to continue? [Y/n] y
Get:7 http://security.debian.org bookworm-security/main amd64 openssh-server amd64 1:9.2p1-2+deb12u3 [456 kB]
Fetched 456 kB in 1s (456 kB/s)        
Download complete and in download only mode
root@server:~#