Upgrade to custom kernel with no multiuser support

I am playing around with kernel customization on my headless Ubuntu Server system. Currently I have 6.8.0-48-generic kernel. My intention is to remove kernel features that I don't need. I decided to start with removing multiuser support so that there would only be root user (mainly to not type sudo for everything). I have built the kernel using my /boot/config-6.8.0-48-generic as a base with disabled CONFIG_MULTIUSER.Disabling this option also removes setuid syscall and turnes out a lot of my existing applications rely on it. During boot process I see a lot of "setuid: Function not implemented"-like messages. The problem is that I don't even get a shell after boot (neither on serial or on an monitor, ssh is also not running). What would be thet steps to proceed further? How can I "tell" the applications that the system is single-user now. Or at least, how can I get a shell? If you intend to reply with something like "this is a security risk" please ignore this post.