Caution: spoilers ahead for No Time To Die
No Time To Die subtly admits the "Bond and Blofeld are brothers" twist from 2015's Spectre was a regretful mistake. Daniel Craig has starred in some of James Bond's best cinematic adventures, but Spectre won't be remembered as one of them. Introducing Christoph Waltz as a perfectly-cast Ernst Stavro Blofeld, Spectre clumsily ties together Craig's previous 3 films and retcons Quantum into a "subsidiary of SPECTRE" to navigate real-world legal obstacles. Arguably Spectre's biggest sin, however, is the dramatic(?) reveal of a sibling connection between Blofeld and James Bond himself.
When Bond became an orphan, he was adopted by Hannes Oberhauser, whose biological son, Franz, would later become the supervillain SPECTRE chief. This means Bond and Blofeld were, for a few short years, foster brothers. The pair enjoyed one more sibling feud for old time's sake in Spectre, before Blofeld returns in No Time To Die, still jailed at Her Majesty's pleasure. Bond interrogates his nemesis over connections to a dangerous new nanobot weapon, but gets riled up when Blofeld admits to sabotaging his relationship with Madeleine Swann. Not realizing he's already infected with the virus-like nanobots, Bond grabs Blofeld in anger and accidentally kills him... and this is where No Time To Die brings up the awkward issue of their sibling history.
In the aftermath of Blofeld's death, the loss is casually dismissed with, "it's a good job he's not a real brother." This could be interpreted as an acknowledgement that Spectre's Blofeld twist was a little bit silly. The line (intentionally, one would assume) highlights the ridiculousness of Bond and Blofeld's sibling link by referencing it in such an offhand, cynical manner. The joke is almost mocking their "brotherhood," which tacitly translates as No Time To Die mocking Spectre's less-than-spectacular Blofeld reveal. No Time To Die's "real brother" gag could also be taken as a meta message to the audience, admitting Bond and Blofeld as foster brothers was a misstep, but effectively saying "it could've been worse - they could've been real brothers."
Quite aside from the timeline confusion caused, James Bond's brotherly relationship with The Artist Formerly Known as Franz Oberhauser undermines Blofeld as a villain. Reducing SPECTRE's criminal activities to the actions of a jealous teenager punishing his foster brother made Blofeld seem petty and feeble, rather than the intimidating mastermind everyone was expecting and hoping for. It was also redundant for Spectre to make such a big deal of Bond and Blofeld's personal connection when, in reality, they only spent a few short years together. That's marginally more dramatic than revealing Rosa Klebb's grandmother lived next door to someone who once dry cleaned James Bond's tuxedo. Then all the niggling questions arise. Why didn't Bond recognize the resurfaced Franz? How would Blofeld have got his revenge if James became an insurance salesman instead of secret agent? And what does Bond and Blofeld being brothers actually add to Spectre's plot?
For better or worse, James Bond has never been shy about making the odd meta remark. George Lazenby famously referred to "the other chap" in 1969's On Her Majesty's Secret Service, after all. Fortunately, No Time To Die is a little more subtle, using Daniel Craig's final film to admit the Blofeld brother twist was bad, and coming as close as is reasonably possible to apologizing without breaking the fourth wall completely. While that doesn't necessarily compensate for Spectre's disappointment, No Time To Die made the right choice by turning Bond and Blofeld's brotherly bickering into a throwaway joke, rather than doubling-down and exploring their history further.