CentOS

The "issues" you will face are that CentOS 7 dies in two months so there will be no more updates for it, security or otherwise. It's a dead distro that should not be used any more and certainly not after 2 months time. Putting a lot of work into updating openssh on it is pointless as the entirety of...

No. And it's not worth the effort of trying either since CentOS 7 goes EOL in less than 2 months time. Pick a new distro and start your migration to it.

CentOS is dead, you need to move to something else.

Check in /proc/cmdline to see if your changes took effect.

CentOS is dead. Use one of the other RHEL rebuilds instead.

https://access.redhat.com/security/cve/CVE-2023-6931 RHEL 7 is listed as "Out of support scope" which means it's too old and the vulnerability not important enough. It also says It is not possible to trigger this issue with the default kernel.perf_event_paranoid sysctl value 2. You may check it with...

Is this a real system or a container?

bash-4.4# ls -laZ /var/lib/tftpboot total 2 drwxr-xr-x. 2 root root system_u:object_r:container_file_t:s0:c128,c144 1024 Jan 4 16:00 . drwxr-xr-x. 15 root root system_u:object_r:container_file_t:s0:c128,c144 1024 Apr 27 15:41 .. -rwxrwxrwx. 1 root root system_u:object_r:container_file_t:s0:c128,c14...

This looks like a question for a samba forum not here.

What are your permissions on /var/lib/tftpboot. Easiest way to show that is to run namei -l /var/lib/tftpboot. Also include the output from ls -laZ /var/lib/tftpboot

First you seem to have set this up in two separate and mutually incompatible ways. Either pick xinetd to start a connection OR run tftpd as a service all the time. Not both. I'd recommend dumping the xinetd bit and disabling that and concentrating on getting it running as a service first. After it w...