I'm by no means an expert in TFTP. I used it for a while when I was dealing with LTSP back before PXE Boot became more widely used. I did find this, however, that /might/ lead you in the right direction. Does the client have a `firewalld` rule as well?

https://blog.thewatertower.org/2019/05/01/tftp-part-2-the-tftp-client-requires-a-firewalld-as-well/

Hope this helps you a little anyway.

Thanks,

Steven Spencer