I saw an answer that you dont recommend group chats with wali for marriage, How about my case where a potential brother might be abroad for my sister and it could be beneficial for them to exchange before or after doing a zoom call. ‏جزاك الله خيرا

A video or voice call in the presence of her wali, so they can see one another and speak before visitation because they are in different countries for example, is allowed. However, be careful of recording, as some people are not trustworthy and might do so. What I do not encourage is exchanging numbers and ongoing private or group chat to get to know each other, even with the wali added. So keep it to what is needed, in the wali's presence, and once you are satisfied, proceed to the next serious step, in shaa Allah.