Install New Tab Start Page and set the custom URL field to https://start.me/ in its settings (and click "save at the bottom of the settings). Then, you use the + button on the tab bar for a home page button. Or, you can use ctrl + t. Then, you use the start page button on the address bar to get to Opera's start page.
And or, you can use Home Button at Top Right, pin its icon to the address bar, and set its homepage to https://start.me/. The icon will be on the right side of the address bar instead of the left though.
Another way is to just think about things differently. Just think of Opera's start page as as home page that has multiple links (via speed dials) on it. You just put https://start.me/ on the start page and you're good. It's 2 clicks instead of one. But, it will become almost involuntary after a while.
You also have the option to enable the bookmarks bar and put https://start.me/ on it. It's a single click that way.
You can also add the site to the sidebar. Goto the URL opera://flags/#sidebar-site-panel, enable the flag, restart Opera, click the 3 dots at the bottom of the sidebar, scroll down to "Custom Site Panels", and add https://start.me/.