Make conversations public by default. If you use Slack, make team channels, project channels, announcement channels etc. all public. Discourage 1:1 and private communication unless really necessary, especially for engineering topics. This single change will have an immense impact on overall company culture.
How to find comfort for and include characters that don't like the spotlight? At least not during early phase/brainstorming. I've worked with many great people that hate to handle things without their usual group first, and will stall until a reasonable approach can be presented. Which means creating shadow communication process - the more you push for "discouraging 1:1" the more they will hide. What your organisatio…
if the issue is that the person is afraid to speak up because of being ridiculed for their ideas, you have a culture problem that needs to be adressed.
if the shy person is new, addressing the problem can be as simple as having the new team member do pair programming sessions with everyone on the team, so that they can get to know everyone better, which will make them more comfortable to speak up. maybe their previous job had a bad culture that influenced their behavior.
those pair programming sessions can also help you identify if there are particular people that cause problems by being intimidating in some way to others. sometimes pair programming can even fix those problems, by allowing the two to get to know each other better and learn to respect each other. that doesn't always work though, and care must be taken that the person who is "afraid" to work with the "bully" is not forced to an interaction they are not comfortable with. if the discomfort is that high a more cautious approach is needed. especially if the person afraid is a long term team member.