The problem for both of them is neither of them appear to have any particular interests or passions. These two are in their early 40's. They need an occupation for the next 30-40 years. How are they to fill their time, (and earn money).
Meghan's main interest seems to be herself. Imagine, the Queen gave her patronage of the National Theatre thinking she would appreciate that, as an actress. But no, not remotely interested as far as one can tell. I think she wouldn't like being surrounded by actors so vastly more talented than herself.
Harry could have so many opportunities - horses - he is happy enough to jump on a polo pony and thrash it up and down the field but is there any evidence of him being interested in horses beyond that? I've taken to watching several American horse trainers/cowboys on YouTube, some of them take on wild mustangs and work miracles. There's an incredible amount of cruelty in the horse trade over there, plus funding for some of the mustang management schemes has been cut. They have kill pens - enough said. One horse rescued from a kill pen was incredibly traumatised and anyway was quite feral, the trainer is so incredibly knowledgeable about horse psychology and has worked an absolute miracle on her over many months, though she will remain with him for life, I doubt she will ever be a safe horse for anyone without his experience and ability to forge a relationship with her. Anyway I digress, but there's plenty Harry could get involved with in the horse world over there if he was interested.
Likewise nature, the national parks. Getting involved with homeless charities or drug rehabilitation.
There's so many things he could get involved with yet he doesn't seem to have any particular interests. The Wales family are hugely sporty, both as fans and players. William started following Aston Villa in his teens and has stuck with the club over the years, developing relationships with players and managers, building knowledge of the game, as well as being President and now Royal Patron of the Football Association. Harry popping up on a podcast to opine on the World Cup just showed the wealth of his ignorance.
Catherine is Royal Patron of the AELTC (Wimbledon) - she and the family love tennis and I'm sure she is very knowledgeable. I think it's lovely that she pops up doing stuff like scanning tickets and chatting to fans as they arrive, working with the chef in the kitchen preparing strawberries, doing some ball boy training with the trainees ahead of the tournament. Meghan doesn't appear remotely sporty and Harry doesn't appear to have any deep passion for any sport - sure a bit of surfing and skiing since he's in California but no regular involvement.
They don't appear to be interested in the arts at all or great readers. Princess Diana loved ballet and was patron of the Royal Ballet School. Princess Margaret was also involved in ballet and the arts.
Most of the Royals have diverse interests and are very knowledgeable about what they love. The Queen obviously with horses but she had many other interests and deep knowledge of all sorts of things. Phillip also had wide interests and knowledge. Princess Anne and her husband love sailing, she learnt a lot from Prince Phillip but obviously Tim also has naval training. I saw an article in some Yachting magazine interviewing her about the boat she and Tim bought (yacht built for them in Falmouth, about £500 K iirc), I think she said they keep it up in Scotland to sail the Western Isles.
Rather than a holiday home in Portugal, where presumably they hide away from prying eyes in their gated complex, living the same life they do in California, why not get a yacht and get into sailing? Much cheaper than a house in Portugal (depending on the choice of yacht obv).
Honestly I don't how they occupy their time let alone what they will do with themselves for the next thirty years. I always think of Harry outside the window juggling as Meghan sat at her big desk/table, with her laptop on a pile of her Bench books. Not sure if that was planned for film footage (showing him as the court jester) or more likely he just has an annoying habit of trying to distract her by fooling around outside the window when she's "working" so she left it in the final Cut to diminish him and show him up.
Remember in South Park when Harry lifted the lid off Meghan and found it empty? The same also applies to him.
A life spent scheming, complaining, demanding attention, it all seems so pointless and unsatisfying. What a way to live.