I've created a custom module to avoid the need to use the "Execute" block. It basically gives you a way to set the pin number, trigger, and callback for the IRQ. You will still create your own function using Blockly.

1. Create a Variable: example "counter"
2. Create a Function:
   1. Name it what you like, example: "count_pulses"
   2. Add single step from Variables: change counter by 1
3. Init PWM0 with your desired pin, freq, and duty
4. Load the attached file under Custom | Open *.m5b file
5. Drag "PIN_IRQ" from Custom onto your workspace
   1. Set the pin number (just an integer, 0 for example)
   2. Set your trigger "machine.Pin.IRQ_RISING"
   3. Set the handler to your function from step 2 above "count_pulses"
6. Add a label if you want and set the loop event to update a label with the current counter value
7. It sounds more complicated than it actually is, check the screenshot

Your resulting code should look vaguely like this:

from m5stack import *
from m5ui import *
from uiflow import *
import machine

setScreenColor(0x222222)

counter = None

label0 = M5TextBox(146, 187, "Text", lcd.FONT_Default, 0xFFFFFF, rotate=0)

from numbers import Number

def count_pulses():
  global counter
  counter = (counter if isinstance(counter, Number) else 0) + 1

PWM0 = machine.PWM(26, freq=25000, duty=50, timer=0)
pin0.irq(trigger=machine.Pin.IRQ_RISING, handler=count_pulses)
while True:
  label0.setText(str(counter))
  wait_ms(2)

Have fun storming the castle!

I agree, it is sad. :(

There is hope, however! I opened up one of the .m5f files that is saved from UI Flow to learn that it is a hybrid json/xml file with all the blockly code represented in XML. I'm thinking of working up a simple script that could be run in browser to parse this data and allow you pull single blocks and merge them into another file.

The concept here is that you upload two files (library.m5f and project.m5f, for examples sake) and then you can pluck whole blocks from and to either file. This way your great new invention from project.m5f can be added to your library and your great work from the library can be added to your project.

It will be simple, dare I say crude, to start with but should help. Also, I did tinker with making a custom .m5b file and it's not that hard but not quite the same as having a pre-built set of routines you want to use all the time. I'll post more info here once I have anything worth playing with.