pxe is working for me in this test virtualbox build.
$ md5sum initrd.img vmlinuz 89251241a484010b98280ce00b3a3763 initrd.img 9261bb24add6bb4ff9ef6aaf348aaf35 vmlinuz
( yum updated )
[centos@localhost ~]$ uname -a Linux localhost.localdomain 4.18.0-193.6.3.el8_2.x86_64 #1 SMP Wed Jun 10 11:09:32 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
[centos@localhost ~]$ cat /etc/redhat-release CentOS Linux release 8.2.2004 (Core)
And it is working here now, too. After replacing the trusty, 8-year old pxelinux.0 with a slightly newer version. Strange that it should break just after C8.1.