There is some information about both visits:
https://archewell.com/news/uplifting-our-military-families/
&
https://archewell.com/news/caring-for-our-veterans/ from the Archewell website.
I bet it was a lovely visit and I'm glad everyone enjoyed themselves.
Also, these types of visit's are just limited to the royals. People with profiles or anyone who has a platform, be it celebrity, humanitarian, philanthropist and etc have been doing these types of visits and events without being royal. Many do it without the bonus or benefit of being royal. Showing up for military servicemen doesn't mean you have to be connected to the military in some official way, it's about showing up and showing support for that community. It isn't reserved for an royal, official or someone who works with the US military, support is support. Such as, Harry might not be in army but he is a veteran that is a founder of an international sporting event that is about service and helping those who are serving or have served. That's more than enough for him to connected to the event.
Even day to day royal work of visiting charities and being patron's of organization's isn't something you have to be royal or royal linked to do. You just have to have a platform and bring attention.
Also, Meghan in 2014 pre-royals worked was apart of the 2014 USO Holiday Tour. Simply as an actress, visiting and shining a light on service people around the world.
I wouldn't see an issue with Brad Pitt showing up either, he's a person with a public platform and the only thing he needs to do is shine a light. He could have family members that served or even simply knew someone that served.
Being there for a community doesn't mean you have to be apart of it, nor do you have work with the US governments. There isn't anything bewildering about the visits they do.
Harry has also released a statement / letter for Scotty's Little Soliders, a charity he has previously supported, ahead of Remembrance Day. It can be found on the Archewell website.
https://archewell.com/news/prince-harry-named-global-ambassador-for-scottys-little-soldiers/
Scotty’s Little Soldiers is a charity that aims to provide relief from the effects of grief for bereaved military children and young people who have experienced the death of a parent who served in the British Forces.
He's also been named the Global Ambassador
https://www.scottyslittlesoldiers.co.uk/duke-of-sussex-remembrance-letter