I installed the Mate Desktop after doing a minimal install of RL9.1 using the RL8.5 instructions for install Mate. The Powertools repo is not needed just epel and those repos enabled by default. It really helps to enable the Cockpit tool so you can copy and paste directly from the instruction page into a terminal. My first attempt failed with missing dependency errors so I inserted --skip-broken thus "
sudo dnf --skip-broken install <long list of packages>"
which then succeeded. Continued the install of followup packages per the documentation enabled the graphical target and rebooted.
The reboot dumped me into an emergency shell due to a switch root problem so I just rebooted again and was able to log in to my Mate desktop.