It seems that updates are not working anymore if the installation has made years ago, so the fix is to edit sources.list as

# 64bit package repository URL's, working as of 01/13/2025
#==================================================================
# Please enable only ONE (1) entry, preferably the first one, nluug !!!
#==================================================================
# rpm http://insecure.nluug.nl/pub/os/Linux/distr/pclinuxos/pclinuxos/apt/ pclinuxos/64bit x86_64 kde6 xfce4 mate
# rpm http://ftp.fau.de/pclinuxos/apt/ pclinuxos/64bit x86_64 kde5 xfce4 mate
# rpm http://mirror.math.princeton.edu/pub/pclinuxos/pclinuxos/apt/ pclinuxos/64bit x86_64 kde6 xfce4 mate # not syncing on this path, not populated on other
# rpm http://pclinuxos.c3sl.ufpr.br/apt/ pclinuxos/64bit x86_64 kde5 xfce4 mate
# rpm http://ftp.cc.uoc.gr/mirrors/linux/pclinuxos/apt/ pclinuxos/64bit x86_64 kde6 xfce4 mate # not syncing since 30 March 2026
rpm http://distrib-coffee.ipsl.jussieu.fr/pub/linux/pclinuxos/apt/ pclinuxos/64bit x86_64 kde6 xfce4 mate
# rpm http://mirror.internode.on.net/pub/pclinuxos/pclinuxos/apt/ pclinuxos/64bit x86_64 kde6 xfce4 mate # appears dead
# rpm http://mirror.aarnet.edu.au/pub/pclinuxos/apt/ pclinuxos/64bit x86_64 kde6 xfce4 mate
# rpm http://ftp.jaist.ac.jp/pub/Linux/PCLinuxOS/pclinuxos/apt/ pclinuxos/64bit x86_64 kde6 xfce4 mate
# rpm http://mirrors.uni-ruse.bg/pclinuxos/apt/ pclinuxos/64bit x86_64 kde6 xfce4 mate
# rpm http://pclinuxos.mirror.wearetriple.com/apt/ pclinuxos/64bit x86_64 kde6 xfce4 mate
# rpm http://mirror.freedif.org/PCLinuxOS/apt/ pclinuxos/64bit x86_64 kde6 xfce4 mate
# rpm http://mirrors.cicku.me/pclinuxos/apt/ pclinuxos/64bit x86_64 kde6 xfce4 mate

**************************************

And do the next thing also.

cp /usr/lib64/apt/methods/http /usr/lib64/apt/methods/https

The source: https://www.pclinuxos.com/forum/viewtopic.php?p=11205#p11205