I know no easy way for advanced customization of notification bubbles. Looks like they simply display provided title and text. I tried command like notify-send "very long title" "very long text" in terminal and was able to reproduce extremely wide bubbles. Title string is probably never autowrapped or cropped with current notification system. I also am able to display more than 5 bubbles.
This is notification area -- an applet in your panel showing application icons and not directly related to notification popups.
What I suggest you trying first is notification center, "the bell icon". It is not a replacement for notification popups, it is a complementary tool provided by UM out-of-the-box.
Check for installation:
apt list --installed | grep indicator-notifications .
If not installed (no output containing "indicator-notifications"), install:
sudo apt install --reinstall indicator-notifications
and restart your session. The bell icon shall appear.
If installed and bell icon is not visible, try:
gsettings set net.launchpad.indicator.notifications hide-indicator false .
If notification center (indicator-notifications) will not fit your workflow, you may try to replace notification system itself. This is probably the hard way. Please, check this thread:
and ask authors whether they managed to make it work in UM 20.04.
Cheers!