Don't be discouraged. It's somewhat hard to brick the m5stack devices. Just do erase again (to be sure), next burn uiFlow v1.6.2 firmware, and then load the latest known working version of your program.

There used to be a way to delete apps from the App menu on the device, but that functionality has been lost in the last few revs of firmware (not sure why). What I typically do is connect to the REPL and manually delete what I want from the /flash/apps directory on the device. Or you could use Thonny or Mu IDE to do the same.

I got everything working...and then I accidently hit ERASE in M5 Burner (ended up uploading a dozen different version of the app trying to get it to work, and read that you only delete apps trough the burner) and now the entire thing is DEAD, doens't react to anything anymore.

…
I have no words.

Seems to work now.

Just one final question - how do I get the values in mmol (as they are on the Nightscout).
I assume it's the SVG value and I saw no conversion in the code itself, which means the SVG is the value in whatever units are used in the US?

Can I just edit a line like this (bolded is changed):
SGVlabel.setText(str((str('') + str(round(sgv / 18),1))))

Yes. Chris-O's dashboard displays the SVG value in mg/dL and it looks like the conversion between mg/dL and mmol/L is to divide mg/dL by 18. So you got it.

Also, I see no alarm sounding in the code, so I added
speaker.sing(240, 10/16)
right under the svg value check for color. Can anyone tell me what the two values represent? I want it really loud.

speaker.sing(frequency, beats) where beats are: 1/16, 1/8, 1/4, 1/2, 1, 2, or 4
you could also do speaker.tone(frequency, duration) where duration is time in milliseconds

For loudness you want speaker.setVolume(int) where int is 0 (no sound) to 1 (full/highest volume). 0.5 is half volume.

Just one final question - how do I get the values in mmol (as they are on the Nightscout).
I assume it's the SVG value and I saw no conversion in the code itself, which means the SVG is the value in whatever units are used in the US?

Can I just edit a line like this (bolded is changed):
SGVlabel.setText(str((str('') + str(round(sgv / 18),1))))

Also, I see no alarm sounding in the code, so I added
speaker.sing(240, 10/16)
right under the svg value check for color. Can anyone tell me what the two values represent? I want it really loud.

I got it working now with her data feed and also made a few improvements to the program. Here you go:
uiFlow file
MicroPython file

Don't forget to change the wifi settings before running on the device.

Ah, okay. It's not actually my data. It is Chris-O's (author of the program). I thought you were still trying to get the app working with Chris' API and couldn't access his data feed (due to some firewall blocking issue, geolocation blocking, etc.).

Let me see if I can figure out how to get his program working with your niece's data feed. Her feed seems to be only missing the dateString, but I'm not sure he's using that anyway. I'm curious though, what does "Tomato" mean in her data feed? Chris' data feed has "share2" at the end.

Region is Europe, Croatia to be more precise

This usully means that you have the same label set for both out puts or the same screen location for both labels.

It's still working for me. What region of the world are you are in?
Can you access the data with a browser? https://tillierscout.herokuapp.com/api/v1/entries?count=1

No glucose display, the only thing all 3 bottuns affect is screen brightness.

basically my screen displays:

SGVIabel (in big letters with DiffSCVI over it)
datalabel
screen brghtness
direction label

and nothing I press or do does anything. Wifi did connect and webpage data is correct.

Turn the developer console on:

After I open the file in uiFlow:

The file at least loads partially. I'm seeing some blocks, but none of the UI labels are showing up on the UI simulator due to the error. So check the Chrome developer console to see if there are other errors you see.

Can you try the Chrome browser and turn on the developer console to see what error it's throwing? Also, did you try the beta uiFlow v1.6.2?

Another way is to copy this python file to your device and place it in the /flash/apps folder. Then after boot up, go to App and select M5Scout-fixed.py from the App List. Don't forget to change the wifi ssid and password before copying the file to your device.

I don't understand why it's not loading or retruning anything. Not even an error message.
Any other way to get a program to M5stack?

The issue with @Chris-0's program is because m5stack changed the screen brightness block in recent firmware versions and Chris has not updated it yet on his GitHub repo. Looking at the Chrome developer console when loading the program into uiFlow, I see this...

TypeError: Unknown block type: screen_set_core_brightness
    at Blockly.BlockSvg.Blockly.Block (scripts.818b820f5fb58046033f.js:1)
    at new Blockly.BlockSvg (scripts.818b820f5fb58046033f.js:1)
    at Blockly.WorkspaceSvg.newBlock (scripts.818b820f5fb58046033f.js:1)
    at Object.Blockly.Xml.domToBlockHeadless_ (scripts.818b820f5fb58046033f.js:1)
    at Object.Blockly.Xml.domToBlockHeadless_ (scripts.818b820f5fb58046033f.js:1)
    at Object.Blockly.Xml.domToBlockHeadless_ (scripts.818b820f5fb58046033f.js:1)
    at Object.Blockly.Xml.domToBlockHeadless_ (scripts.818b820f5fb58046033f.js:1)
    at Object.Blockly.Xml.domToBlockHeadless_ (scripts.818b820f5fb58046033f.js:1)
    at Object.Blockly.Xml.domToBlockHeadless_ (scripts.818b820f5fb58046033f.js:1)
    at Object.Blockly.Xml.domToBlockHeadless_ (scripts.818b820f5fb58046033f.js:1)

The block changed from screen_set_core_brightness to screen_set_brightness. I fixed the file for you and now it loads properly in the online uiFlow IDE v1.6.2. You can find the modified file here.

@Chris-0 did a project for Nightscout here

I cannot seem to find an app or code to upload to m5 stack for that.
Nor can I find anything in the already present app or settings.

I do have a .ini file with the basic settings (and nightscou site info, SSD data, etc..), but no microSD card.