Notion - Inline Math for the Desktop App (credit https://www.notion.so/Notion-Hacks-27b92f71afcd4ae2ac9a4d14fef0ce47)

inlinemath-userscript.js

// ==UserScript==
// @name Inline Math for Notion.so
// @homepageURL https://www.notion.so/evertheylen/Notion-Inline-Math-9c5047a4e7c84643848b3630db8d5a5e
// @version 0.2.1
// @match https://www.notion.so/*
// @grant GM_addStyle
// @require https://cdn.jsdelivr.net/npm/katex@0.10.0/dist/katex.js
// ==/UserScript==

// Instructions for use:
//   - Make sure you have at least one normal math block on your page
//   - Use inline code starting with "math:". For example: `math: f(x) = x^2`
//   - Press F2 to rerender all inline math. You can of course change the shortcut in the code below.
//   - The inline math will revert to inline code when the block becomes active.

const subscript = /_(?!{)(.+?)(?:_|(\^|$| ))/g
const superscript = /\^(?!{)(.+?)(?:\^|(_|$| ))/g

GM_addStyle(`
.notion-frame span .katex {
    padding-right: 0 !important;
    font-size: 1.3em;
}
`)

function rerender_all(e) {
    document.querySelectorAll("body").innerHTML = "";
    var code = document.querySelectorAll('span[style*="monospace"]');
    code.forEach(function(el) {
        if (document.activeElement.contains(el)) {
            if (e.key != "F2") {
                return;
            }
        }
        var s = el.textContent;
        if (s.startsWith("math:")) {
            el.style.color = null;
            el.style.background = null;
            s = s.slice(5).trim();
            katex.render(s, el, {throwOnError: true, font: "mathit"});
        } else if (s.startsWith(",")) {
            el.style.color = null;
            el.style.background = null;
            s = "\\mathrm{" + s.slice(1).trim() + "}";

            var match;
            while (match = s.match(subscript)) {
                s = s.replace(subscript, "_{$1}$2");
            }
          
            while (match = s.match(superscript)) {
                s = s.replace(superscript, "^{$1}$2");
            }        

            katex.render(s, el, {throwOnError: true, font: "mathit"});
        } else if (s.startsWith("$")) {
            el.style.color = null;
            el.style.background = null;
            s = s.slice(1).trim();
            katex.render(s, el, {throwOnError: true, font: "mathit"});
        }
    });
}

function rerender() {
    rerender_all({key: "discard"});
    setTimeout(rerender, 500);
}
setTimeout(rerender, 5000);

window.addEventListener("mousedown", rerender_all);
window.addEventListener("keydown", rerender_all, true);

inlinemath.js

const subscript = /_(?!{)(.+?)(?:_|(\^|$| ))/g
const superscript = /\^(?!{)(.+?)(?:\^|(_|$| ))/g

window.onload = function(e) {
    loadJS(
        "https://cdn.jsdelivr.net/npm/katex@0.10.2/dist/katex.min.js",
        function() {
            rerender_all();
        },
        document.body
    );

    let customCSS = document.createElement("style");
    customCSS.innerHTML = `.notion-frame span .katex {
            padding-right: 0 !important;
            font-size: 1.3em;
        }`;
    document.getElementsByTagName("head")[0].appendChild(customCSS);
};

var loadJS = function(url, implementationCode, location) {
    //url is URL of external file, implementationCode is the code
    //to be called from the file, location is the location to
    //insert the <script> element

    var scriptTag = document.createElement("script");
    scriptTag.src = url;

    scriptTag.onload = implementationCode;
    scriptTag.onreadystatechange = implementationCode;

    location.appendChild(scriptTag);
};

function rerender_all(e) {
    document.querySelectorAll("body").innerHTML = "";
    var code = document.querySelectorAll('span[style*="monospace"]');
    code.forEach(function(el) {
        if (document.activeElement.contains(el)) {
            if (e.key != "F2") {
                return;
            }
        }
        var s = el.textContent;
        if (s.startsWith("math:")) {
            el.style.color = null;
            el.style.background = null;
            s = s.slice(5).trim();
            katex.render(s, el, {throwOnError: true, font: "mathit"});
        } else if (s.startsWith(",")) {
            el.style.color = null;
            el.style.background = null;
            s = "\\mathrm{" + s.slice(1).trim() + "}";

            var match;
            while (match = s.match(subscript)) {
                s = s.replace(subscript, "_{$1}$2");
            }
          
            while (match = s.match(superscript)) {
                s = s.replace(superscript, "^{$1}$2");
            }        

            katex.render(s, el, {throwOnError: true, font: "mathit"});
        } else if (s.startsWith("$")) {
            el.style.color = null;
            el.style.background = null;
            s = s.slice(1).trim();
            katex.render(s, el, {throwOnError: true, font: "mathit"});
        }
    });
}

function rerender() {
    rerender_all({key: "discard"});
    setTimeout(rerender, 500);
}
setTimeout(rerender, 5000);

window.addEventListener("mousedown", rerender_all);
window.addEventListener("keydown", rerender_all, true);

patcher.sh

( cd /Applications/Notion.app/Contents/Resources; asar extract app.asar app )

# cp inlinemath.js /Applications/Notion.app/Contents/Resources/app/renderer/inlinemath.js

# sed -i '' 's/<\/head>/<script src="inlinemath.js"><\/script><\/head>/g' /Applications/Notion.app/Contents/Resources/app/renderer/index.html

echo "\n" >> /Applications/Notion.app/Contents/Resources/app/renderer/preload.js
cat inlinemath.js >> /Applications/Notion.app/Contents/Resources/app/renderer/preload.js

Can someone please walk me through installing this? I have no idea what to do, thanks.