Oddly enough when I got the booster it didn't do much. But when I got my flu shot about a month later I got the worst localized reaction to a vaccine I've ever had.
I do wonder if there's some correlation between getting a flu shot close ish to the booster
I probably know about as much about medicine as you know about English Championship soccer, but if I had to guess I would wonder if the antibodies produced to combat the flu are similar to those that combat covid given the similarities between the two viruses, and thus your immune system already being in battle mode as a result of your booster meant that the flu reaction to the flu shot was more extreme.
On a related note, I'm actually going to get a flu shot this year. Never have before, but I guess like many I've become much more educated as to the societal responsibility of getting vaccinated.