The day of the week starts on Monday and not on Sunday.

It looks like you've modified the code in this post (https://forums.garmin.com/developer/connect-iq/f/discussion/272964/current-day-of-the-week-in-an-ellipse/1311736#1311736). I see that you've made some changes, but I'm going to look at the original code.

The original code is supposed to print the days of the week (in the device's language) starting with Monday, and highlight the current day. e.g.

Mon
Tue
Wed
Thu
Fri
Sat
Sun

On the sim in my computer, it prints the Sun as the first day. This is due to a bug in the original code relating to time zones (*) -- to fix this, wherever you see "Time.Gregorian.info", replace it with "Time.Gregorian.utcInfo", in drawDay(): change "Time.Gregorian.info", replace it with "Time.Gregorian.utcInfo"

(You'll find that if your system timezone is west of UTC -- e.g. UTC-5 / Eastern Time -- the the first day of the week displayed will be Sunday. Any other timezone -- such as UTC, UTC+1, etc -- will work as expected. This is because the original code uses January 3, 2000 00:00 UTC as a reference date for Monday, but it grabs the day of week in *local time* for that reference date, when it should be getting the day of the week in *UTC time*. In other words, in UTC time, January 3, 2000 00:00 UTC is always a Monday. In local time, January 3, 2000 00:00 UTC is a Monday or a Sunday depending on your local time zone.

I changed my PC's time zone to UTC+0, restarted eclipse, re-ran the app, and the original code displayed Monday first.)

Even after this fix, the code also has a bug where if it's currently Sunday, the highlight rectangle is placed in the empty space above Monday, instead of around Sunday.

To fix this problem, you need to add a couple of lines of code after "var dayOfWeekNumber = ...  //week starts on Sunday, not Monday"

        var dayOfWeekNumber = Time.Gregorian.utcInfo(date, Time.FORMAT_SHORT).day_of_week - 1; //week starts on Sunday, not Monday
        if (dayOfWeekNumber == 0) { // <=== new code
               dayOfWeekNumber = 7; // <=== new code
           } // <=== new code

Here's the full drawDay() and highlightDay() functions with the fixes described above. I've also included the original onUpdate(), for reference, as well as other relevant code (with an added comment for Gregorian.moment()).

(In the code below, the var names localDate and utcDate are little misleading as the format of the input is the same in both cases (each date is a Time.Moment which represents the numbers of seconds since January 1, 1970 at 00:00:00 UTC), but the actual difference is the format of the output: in the case of utcDate, we want to show the day of the week in UTC time, since the input was initialized based on UTC time, and in the case of localDate, we want to show the day of the week in local time, since that's what's relevant to the user.)

    // ...
    
    var fontSize = Graphics.FONT_XTINY;
    var paddingWidth=6; //padding around the text
    var paddingHeight=2; //padding around the text
    var daysX = 0.5; //middle of the screen
    var ySpacing = 0.1; //how much of the screen to leave vertically. The larger the number the greater the spacing
    
    // Note that the args to Gregorian moment are assumed to be in UTC time
    // See: https://developer.garmin.com/connect-iq/api-docs/Toybox/Time/Gregorian.html#moment-instance_function
    // Therefore, KNOWN_MONDAY is January 3, 2000 00:00 UTC
    // and any code which extracts the day of week based on KNOWN_MONDAY
    // should use Gregorian.utcInfo(), not Gregorian.info()
    var KNOWN_MONDAY = Gregorian.moment( {:year=> 2000, :month=> 1, :day=> 3});
    var DAY_LENGTH = 3600 * 24;

    // ...

    function onUpdate(dc as Dc) as Void {
        
        //clear the screen
        dc.setColor(Graphics.COLOR_RED, Graphics.COLOR_BLACK);
        dc.clear();
        dc.setPenWidth(2);
                
        //draw all the days of the week down the screen
        drawDay(dc, 1, KNOWN_MONDAY);
        drawDay(dc, 2, KNOWN_MONDAY.add(new Time.Duration(1 * DAY_LENGTH)));
        drawDay(dc, 3, KNOWN_MONDAY.add(new Time.Duration(2 * DAY_LENGTH)));
        drawDay(dc, 4, KNOWN_MONDAY.add(new Time.Duration(3 * DAY_LENGTH)));
        drawDay(dc, 5, KNOWN_MONDAY.add(new Time.Duration(4 * DAY_LENGTH)));
        drawDay(dc, 6, KNOWN_MONDAY.add(new Time.Duration(5 * DAY_LENGTH)));
        drawDay(dc, 7, KNOWN_MONDAY.add(new Time.Duration(6 * DAY_LENGTH)));
       
        //draw the ellipse around that day
        highlightDay(dc, Time.now());
    }
    
    function drawDay(dc, position, utcDate){
        // We use utcInfo() because utcDate was initialized using a
        // date specified in UTC time (KNOWN_MONDAY)
        var name = Time.Gregorian.utcInfo(utcDate, Time.FORMAT_MEDIUM).day_of_week;
        dc.drawText(daysX * dc.getWidth(), position * ySpacing * dc.getHeight(), fontSize, name, Graphics.TEXT_JUSTIFY_CENTER|Graphics.TEXT_JUSTIFY_VCENTER);
    }
    
    function highlightDay(dc, localDate){
        // We use info() because we want to display the date in the user's
        // local time zone
        var dayOfWeekNumber = Time.Gregorian.info(localDate, Time.FORMAT_SHORT).day_of_week - 1; //week starts on Sunday, not Monday
        if (dayOfWeekNumber == 0) {
       		dayOfWeekNumber = 7;
       	}
        var dayOfWeekName = Time.Gregorian.info(localDate, Time.FORMAT_MEDIUM).day_of_week;
             
        //calculate the width of the ellipse for the length and height of the name eg. "SUN"
        var width = dc.getTextWidthInPixels(dayOfWeekName, fontSize) + paddingWidth;
        var height = dc.getFontHeight(fontSize)+paddingHeight;
        
        //position the elipse in the middle of the screen
        var xPosition = dc.getWidth()/2 - width/2;
        //and the right number of days down
        var yPosition = dayOfWeekNumber * ySpacing * dc.getHeight() - height/2;
                
        //draw it
        dc.drawRoundedRectangle(xPosition, yPosition, width, height, 3); 
    }