if i know a colleague is uncomfortable to speak in a group i can collect their ideas in person, and share it with the group, but ideally the protocol should be public. so create a public chat group with only the two people joining.

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.