I'm missing the Categories for SF Symbols.
I think there are only Categories in the Mac App.
I found two older version and a Screenshot for the new Gaming Cat.
I add some cats for newer Symbols, but didn't finished.
This is what i have (with Pythonista Symbols and Emojis)

Icons.json

Names of restricted Symbols are here:
/System/Library/CoreServices/CoreGlyphs.bundle/symbol_restrictions.strings
(also a plist file)

If someone interested in a list of string, here we go

import plistlib
import io

vFilePath = '/System/Library/CoreServices/CoreGlyphs.bundle/symbol_order.plist'

with open(vFilePath, 'rb') as vFile:
    vFileObject = io.BytesIO(vFile.read())
vJsonSFSymbols = plistlib.load(vFileObject)

for vIndex, vJsonSFSymbol in enumerate(vJsonSFSymbols):
    print(str(vIndex).zfill(4), vJsonSFSymbol)

@cvp
I think all shortcut actions goes through the new compact UI.
And if your shortcut has no User Input / Output there should be only one message that the shortcut is running.

I hope this stops in near future:

Custom App Icons on Home Screen No Longer Route Through Shortcuts App in iOS 14.3 Beta 2

You can test the ios font and their glyphs with a short script:

from objc_util import *

UIFont = ObjCClass('UIFont')
vObjCAllFontNames = []
vObjCFontFamilieNames = UIFont.familyNames()
for vObjCFontFamilieName in vObjCFontFamilieNames:
    vObjCFontNamesWithinFamily = UIFont.fontNamesForFamilyName_(vObjCFontFamilieName)
    vObjCAllFontNames += vObjCFontNamesWithinFamily

vFontFamilieNames = []
vAllFontNames = []

for vTemp in vObjCFontFamilieNames:
    vFontFamilieNames.append(str(vTemp))
for vTemp in vObjCAllFontNames:
    vAllFontNames.append(str(vTemp))

vAllFontNames.sort()
for vFont in vAllFontNames:
    vConsoleFont = [(vFont, 20), (0, 0, 0)]

    console.set_font(vConsoleFont[0][0], vConsoleFont[0][1])
    console.set_color(vConsoleFont[1][0], vConsoleFont[1][1], vConsoleFont[1][2])

    print(vConsoleFont[0][0])
    print(u'\u0048\u0065\u006c\u006c\u006f \u0057\u006f\u0072\u006c\u0064\u003a \u10c5\u10c7\u10cd\u10d0\u000a')

console.set_font()
console.set_color(0.00, 0.00, 0.00)

Maybe this is a help for you, but i didn't test it.
FontInstaller

You can Start a Shortcut with Pythonista:

import webbrowser
vUrl = 'shortcuts://run-shortcut?name=testStartWithUrlScheme&input=10'
webbrowser.get('safari').open(vUrl)

Maybe you can split your Shortcut into 2 different Shortcuts.
This should work, if you use Url Scheme on both sides.
(it's not really in the Bachground, as cvp mentioned)

This works for me, the script is in This iPad/dir:

The iCloud Path should be:
/private/var/mobile/Library/Mobile Documents/iCloud~com~omz-software~Pythonista3/Documents

but i dont use parameter

Edit:
Did a test for parameter with url scheme:
see here: Pythonista Url scheme

works too

Not iPadOS 14. Nothing is working. 😩
The only Safari Link i get is:
localhost:49402
second try:
localhost:49404

then yes :)

@DavinE,

I think it is a Pythonista Problem with iPadOS 13+

Btw: you have 2 different Browser:
iPhone: iPhone (with standard mobile Websites)
iPadOS: Macintosh (with standard desktop Websites)