First question I have no idea
Second question yields another question
Did you after initially setting up your panels go to MATE Tweak and save your layout? If so Control Center MATE Tweak Panel and under Panels scroll to your saved Panel
My panel configuration is located at
/usr/share/mate-panel/layouts/{your panel layout} but yours won't be there if you didn't save.
I have a Calc Spreadsheet with all my odds and ends (one sheet with panel applets (have 48 on bottom panel and 16 on top) so when doing a complete install just go down the list to set everything to my liking.
Panels have been very stable so far for me. I use MATE for the panels and the ability to place lots of icons on Desktop as I work there and then save to custom locations (1 folder with folders for data from each application)
Seems like Gnome you have to add a program/app to use icons on Desktop.
Note on image in my layout folder the rest are there but I think without Welcome they don't show up on my system in MATE tweak and don't know how to enable them. Not using so no big deal for me.
Edit
Found that removing Snap and Welcome was not the reason for multiple layouts not showing in MATE Tweak on my system. Per this post
https://ubuntu-mate.community/t/ubuntu-testing-week-ubuntu-mate-20-10/22259/33?u=mendy
found solution or workaround. Checked in Synaptic and found that for whatever reason indicator-datetime was not installed and indicator-session was. Installed and now have full list of layouts. Sorry for wrong information above concerning showing of layouts in Tweak.
