Hi,
I have the “create event icon” placed to the right and outside the +menu, but you can place it to the left with those instructions :
1° In your theme’s header in admin>appearance>theme>edit>edit code>head add this javascript
<!-- Custom Create Event Button (Icon-based, Language-proof) -->
<script>
(()=>{const e=".d-editor-button-bar",t=".btn.no-text.fk-d-menu__trigger.toolbar-menu__options-trigger.toolbar__button.options.toolbar-popup-menu-options",n=".fk-d-menu__inner-content",o=".d-modal.fk-d-menu-modal",c=e=>{const t=e.querySelector('svg use[href="#calendar-day"]');return t?t.closest("button"):null},r=(e,t,n=4e3)=>new Promise((o,c)=>{const r=t(e);if(r)return o(r);const l=new MutationObserver(()=>{const n=t(e);n&&(l.disconnect(),o(n))});l.observe(e,{childList:!0,subtree:!0}),setTimeout(()=>{l.disconnect(),c()},n)}),l=(e=4e3)=>{const t=new MutationObserver(()=>{document.querySelector(o)&&t.disconnect()});t.observe(document.body,{childList:!0,subtree:!0}),setTimeout(()=>t.disconnect(),e)},s=e=>{if(e.querySelector(".custom-create-event-btn"))return;const o=document.createElement("button");o.className="btn no-text btn-icon toolbar__button link custom-create-event-btn",o.title="Create event",o.innerHTML='<svg class="fa d-icon d-icon-calendar-day svg-icon"><use href="#calendar-day"></use></svg>',e.appendChild(o),o.addEventListener("click",async()=>{const e=document.querySelector(t);if(!e)return;e.click();let o=document.querySelector(n);o||(await new Promise((e,t)=>{const c=new MutationObserver(()=>{(o=document.querySelector(n))&&(c.disconnect(),e())});c.observe(document.body,{childList:!0,subtree:!0}),setTimeout(()=>{c.disconnect(),t()},2e3)}));try{(await r(o,c)).click(),l()}catch{}})},u=new MutationObserver(()=>{const t=document.querySelector(e);t&&s(t)});u.observe(document.body,{childList:!0,subtree:!0});const d=document.querySelector(e);d&&s(d)})();
</script>
2° if you want the icon to the left and not to the right : on the same admin page you will find a CSS tab where you may add this there :
.btn.no-text.btn-icon.toolbar__button.link.custom-create-event-btn { order: -1; }
3° Bonus : if you want this button to be visible at this place into only certain categories use the script there and modify the conditions with your categories names Discourse Calendar (and Event) - #547 by opcourdis