To help you answer this question, let me first of all define what is usually considered as Generation Z. Generation Z are people who are born between 1997 and 2012, which means that today members of this generation are between 9 and 24 years old.
Due to Covid-19, it has become as good as impossible to travel not only abroad, but during lockdown it has even become impossible (or at least very difficult) to travel outside one's local area.
Let us first of all look at the restrictions of travel on a national and local level. This has been a concern especially for Generation Z because of the fact that this generation is at the age where social interaction with friends is very important and independence from parents is part of normal developmental progress, particularly for those who are in their teenage years and older. Being restricted with regard to where they can go has therefore had a massive impact on this generation, as it made it very difficult for them to meet their friends, for example. Instead, they are forced to stay at home with their family, with online chats being the only way to communicate with friends. This is in total contradiction to what they would usually want to do. Therefore, for some members of Generation Z, this restriction and lack of freedom has led to severe problems both emotionally and psychologically.
With regard to the limitations on international travel, you could say that this has particularly impacted on Generation Z because this generation has grown up with a lot of freedom up until this point. Many children have grown up going on holidays with their family or with their friends, which is suddenly no longer possible. For some, this restriction of free movement has led to severe anxiety attacks.
You might also want to mention that travelling to different places used to be a normal part of the learning process when growing up. Seeing new places, meeting new people and making new experiences whilst on holiday have all been part of many young people's development up until recently. With the advent of COVID-19, this learning opportunity has been massively reduced and, as a result, Generation Z will have missed out on a massive opportunity for further intellectual development.