Hi, fellow introvert.
I can't speak for every introvert, because each and every one of us is different; hence, each has a different approach on how to break through their bubbles.
You can first ask yourself: what is your aim in wanting to leave behind your bubble, what is the goal you want to achieve in doing so? Is it because you want to explore a different side of yourself? Challenge yourself? Is it because you are bored and tired of your normal routine, and you want to experience fresh, new experiences? Or is it because you are forced to?
If you have a strong enough reason to do so, then naturally, you would find the courage, and the motivation to do things, even things that you normally disliked doing. But if you are forced to, then ask yourself once more: Is it necessary? If yes, then the same applies as well, you will naturally find your motivation.
In terms of practical tips, I would say: take it slowly. Don't start by going to a bar and talk to random strangers, or go on a socializing spree, that would only tire you out, or make you even more reluctant to continue.
Maybe you can start by speaking out more during meet-ups, voicing your opinions on things etc. Small talk can be challenging because you might need to constantly come up with new topics, but instead of saying stuff for the sake of saying stuff, maybe you can ask others about themselves, that would get them talking. People like to talk about themselves.
When it comes to going outdoors, you can set yourself a schedule. For example, every Saturday, instead of staying at home, you can arrange for a weekly gathering with different groups of friends, or enroll yourself in classes or clubs, to meet with other like-minded people (or strangers).
Hope this helps.