Support for monarchy going down from 67% to 63% isn't a huge dive but combined with an increase of 21% to 25% for a preference for a republic is still a considerable effect probably related to Harry and Meghan's attacks on the monarchy.
I guess the drop in support from 67 to 63 % is at the limit of the maximum margin of error, which means that it could still be a sampling error only, but, most likely, indicates some real movement in public opinion, albeit small.
I would be more curious to see the impact the interview had in other Commonwealth realms where support for the republic is stronger than in the UK. We have already seen pro-republic politicians using the interview to attack the monarchy in Australia, Barbados and Jamaica for example.
It could also be related to Harry stating that his father no longer took his phone calls (if I understand it correctly, that referred to the period they were in Canada before their bombshell announcement) or how he described that they were 'suddenly' left hanging after Charles quit paying for their upkeep and security.
I am not British, but, to me, the argument that they were cut off and had their security taken away is the one I would the least sympathize with. The idea that Harry would continue to get paid UK state security while he and his family were living full time as private citizens overseas is obviously unreasonable and the fact that Harry doesn't see that only suggests a sense of entitlement and lack of realism. The Canadians on the other hand apparently provided RCMP security to the Sussexes for almost five months (from November to March ?) until there was the so-called "change of status" after which they no longer qualified under current rules in place in Canada for public protection and Canadian public opinion was apparently opposed to their continuing to get state security paid for by Canada.
I think the jury is still out there on whether bailing out and going to the USA to pursue a private career was always Meghan's plan all along or not, but, to be fair to the Sussexes, what they told in the Oprah interview is that their initial plan was to stick with the role of full-time royals in the UK for life, but that became impossible when Meghan's mental health and even life were at risk. Then, they tried the "half-in, half-out" solution where they claim they genuinely believed they could continue to serve the Crown in some unspecified (and, I would add, unrealistic) role in a country in the Commonwealth (Harry, i think, mentioned New Zealand, Canada, or South Africa, which is not even a realm BTW, in the Oprah interview). When that plan was rejected and they were cut off, they allege they had to run away to California for safety reasons.
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