The zeroqode template is great for a completely custom version, or if you want the one Bubble uses it’s called Discourse, but is quite expensive: https://www.discourse.org/
You can self-host Discourse for free. From its web:
Good news! Discourse is, and will always be, 100% free and open source software. You may also want to self-host for reasons other than budget, including privacy or full control over the free software that you’ve installed. Here’s how you can install it yourself on your own server.
Alternatively, the community can install Discourse in the cloud for you for a flat one-time fee. Please note that a $5/month hosting fee is still payable to the cloud provider (Digital Ocean), and that this option is completely self-support after the initial install. Click here to purchase a self-supported community install.
I’m not sure - never used it myself but I think it works just out of the box. There is a resource in the manual for it somewhere - search Discourse in the Bubble reference guide