Comment 4 for bug 1697273

Version for Jammy maybe patched as follows

cat <<EOF > meld.patch
--- /usr/share/meld/ui/filediff.ui
+++ /home/j/filediff.ui
@@ -24,6 +24,7 @@
         <property name="stock_id">gtk-revert-to-saved</property>
         <signal name="activate" handler="on_revert_activate" swapped="no"/>
       </object>
+ <accelerator key="R" modifiers="GDK_SHIFT_MASK | GDK_CONTROL_MASK"/>
     </child>
     <child>
       <object class="GtkAction" id="SplitAdd">
EOF
sudo patch /usr/share/meld/ui/filediff.ui < meld.patch

I'll create a PPA in near future for my personal needs.