Reminders

[I found this which looks like it may do the job and has a gui https://habr.com/ru/articles/240245/]

Reminder apps seem to be either

• bloated and unable to do simple reminders
• need to have some app running all the time (like thunderbird)
• Use google
• Be completely out of date and broken dependencies (Orage was fine otherwise)
• Use the system notifications which are not persistent and ignore all attempts to change that.

What’s the point of a reminder if you have to remember to look for it?

Here is a script that goes some way to fixing this.

• First, add a line source ~/apps/scripts/remind.sh to the .bashrc file (path to wherever you put the script) so that it loads on login.
• Or see below how to check first that remind.sh exists.
• Check you have atd installed and if not install it. sudo apt install at
• Make sure it will run on login. systemctl enable --now atd

#!/usr/bin/env bash
function remind () {
  local COUNT="$#"
  local COMMAND="$1"
  local MESSAGE="$1"
  local OP="$2"
  shift 2
  local WHEN="$@"
  # Display help if no parameters or help command
  if [[ $COUNT -eq 0 || "$COMMAND" == "help" || "$COMMAND" == "--help" || "$COMMAND" == "-h" ]]; then
    echo "COMMAND"
    echo "    remind <message> <time>"
    echo "    remind <command>"
    echo
    echo "DESCRIPTION"
    echo "    Displays notification at specified time"
    echo
    echo "EXAMPLES"
    echo '    remind "Hi there" now'
    echo '    remind "Time to wake up" in 5 minutes'
    echo '    remind "Dinner" in 1 hour'
    echo '    remind "Take a break" at noon'
    echo '    remind "Are you ready?" at 13:00'
    echo '    remind list'
    echo '    remind clear'
    echo '    remind help'
    echo
    return
  fi
  # Check presence of AT command
  if ! which at >/dev/null; then
    echo "remind: AT utility is required but not installed on your system. Install it with your package manager of choice, for example 'sudo apt install at'."
    return
  fi
  # Run commands: list, clear
  if [[ $COUNT -eq 1 ]]; then
    if [[ "$COMMAND" == "list" ]]; then
      at -l
    elif [[ "$COMMAND" == "clear" ]]; then
      at -r $(atq | cut -f1)
    else
      echo "remind: unknown command $COMMAND. Type 'remind' without any parameters to see syntax."
    fi
    return
  fi
  # Determine time of notification
  if [[ "$OP" == "in" ]]; then
    local TIME="now + $WHEN"
  elif [[ "$OP" == "at" ]]; then
    local TIME="$WHEN"
  elif [[ "$OP" == "now" ]]; then
    local TIME="now"
  else
    echo "remind: invalid time operator $OP"
    return
  fi
  # Schedule the notification
  echo "notify-send '$MESSAGE' 'Reminder' -u critical" | at $TIME 2>/dev/null
  echo "Notification scheduled at $TIME"
}

And/or use xcowsay ${MESSAGE} | at $TIME 2>/dev/null

We can check to see if remind.sh exists first as well in the .bashrc

if [ -f ~/apps/scripts/remind.sh ]; 
then
    source ~/apps/scripts/remind.sh
else
    echo "File Not Found: ~/apps/scripts/remind.sh"
    # ... other error handlings
fi

For more, including sourcing multiple files and checking all, see this page.
Notifications script is here.
For additional time formats etc for the at command, see this page.