Meghan's biggest problem is that she refused to take any advice or help with the role and that she has this innate need to be acknowledged as the expert on everything.
She was offered Sophie (now Duchess of Edinburgh) as a mentor ... refused by Meghan.
The Queen requested Samantha Cohen guide them with her 17 years experience as the Queen's own press secretary - it was meant to be 6 months transitional help but she stayed 18 months because they couldn't get a replacement - Cohen has since said the role was like working with teenagers.
The Queen offered her one of her own experienced equerries, Lt. Col. Nana Kofi Twumasi-Ankrah but this was rejected by Meghan as "insulting". Meghan's friend and author Omid Scobie wrote “Though a charming and intelligent man, it stood out like a sore thumb to Meghan and her friends,”
I think with retrospect we can see what a huge job the Palace staff did with Harry. A decade ago Harry was a popular royal and believed to be friendly and charming through a carefully curated palace image that involved him mostly working with his own interests - the military, playing polo, Africa - or some combination of these. Since he dropped out of royal life, and despite paying millions to top rated US PR firms such as Sunshine Sachs and WME - Harry's image is mostly as a bitter and miserable man who makes his money whining about his family.