--full-generate-key presumably ends up calling ask_keysize(), which does not take opt.flags.large_rsa into account the way that gen_rsa() appears to. This results in the keysize being limited to 4096 instead of 8192 as expected.
I am familiar with the security ramifications of using an 8192 bits RSA key, but I saw this as an implementation flaw and thought it would be worth officially reporting as I know others have encountered issues doing so both in the past and to date (just search "gpg create 8192 rsa key").

To reproduce: gpg --full-generate-key --enable-large-rsa

Please select what kind of key you want:
   (1) RSA and RSA (default)
   (2) DSA and Elgamal
   (3) DSA (sign only)
   (4) RSA (sign only)
  (14) Existing key from card
Your selection? 1
RSA keys may be between 1024 and 4096 bits long.
What keysize do you want? (3072) 8192
RSA keysizes must be in the range 1024-4096
What keysize do you want? (3072)

Debian 11.5, GnuPG 2.2.27 or build tag gnupg-2.2.27 w/ --enable-large-secmem