They also fixed a few other odds & ends like how Female Indeedee could only get Trick Room through Raids, despite Male Indeedee still learning it through TM.
Worth bringing up: this was obviously addressing a mistake, but not exactly the mistake you think!
Indeedee-F
not learning the TM was the intended behavior to begin with and has always been an intentional difference between the forms, even in Gen VIII; the raid giving it to the female form at all is the part that was an error.
To compare: in Gen VIII, male Indeedee got all of the room moves to itself (Trick Room, Magic Room and Wonder Room) while female got exclusive access to the screen moves instead (Reflect, Light Screen and Safeguard); male got Power Split and Power Swap and female got Guard Split and Guard Swap; and they each had exactly five other exclusive moves that are a bit harder to fit into neat parallels: male got After You, Encore, Extrasensory, Last Resort and Tri Attack, while female got Baton Pass,
Follow Me (!!!!!!), Heal Pulse, Healing Wish and Psycho Shift.
The list of movepool differences between the two got a bit smaller this Gen with the different TM list, but they would still have had an equal number of exclusive moves (seven each) if female didn't get Trick Room, while the mistake of giving it Trick Room gave them a more lopsided six exclusive moves (male) to seven exclusive moves (female). This bit doesn't really mean anything in terms of "fairness" or whatever when you compare the quality of their moves, but I think it does help to clarify the "vision" behind the duo's movepools and reinforce that it was intentional for Indeedee-F to miss out on Trick Room.
More from the point of view of analyzing gameplay, the female form was already
drastically better of the two in VGC because of its better bulk and the incredible value and scarcity of Follow Me alone compared to basically any of the other moves that were exclusive to either form.
Moreover, the absence of Trick Room was arguably an interesting drawback compared to the increasingly long list of supportive Psychic/Normal-types - not only the other Indeedee but also Oranguru, Wyrdeer and Farigiraf, which are all in SV and all made for VGC
(I know Oranguru saw usage in at least one of the SM series, and Farigiraf has actually been doing pretty well for itself too this year, which I love). These are all sidegrades of a similar archetype and basically all value Trick Room a great deal as their primary role on a team, but Indeedee-F, which might well have been the best of the bunch even without Trick Room or at least been reserved for a different style of team, was very much intended to create a meaningful tradeoff by leaving it out.
As for how the mistake took place and why it stuck:
first of all, the two Indeedee forms have distinct 3* raids that account for their movepool differences, but their 5* raids instead have an identical moveset that just happened to be legal for the male and not for the female, implying that the Indeedee-F raid that started all of this might have just... been wrongly copy-pasted from Indeedee-M by someone who didn't know any better. P: Like, this is entirely understandable and a
really easy thing to overlook, so I can't blame them; look at how many people assume that it not learning the move is the part that was a mistake in the first place.
Once that happened, retconning its TM compatibility was the only reasonable response - I mean, there wasn't really anything else they could do. Trick Room
has been competitively run on Indeedee-F throughout VGC so far (and it's a unsurprisingly a really big deal on it), and obviously people already have it, so it's not really something you can just sweep under the rug by fixing the raid itself. At that point, I'm sure Game Freak must have felt it was better to make it more accessible, because the alternative would be to do nothing and leave it in this weird state of "technically legal, very competitively relevant, but super obscure and unnatural to get."
I regret that it kinda messed with what might have been a really clean competitive dynamic, and I feel like Indeedee-F definitely oversteps the boundaries it was designed for by having it, but I mean... I'm sure the designers feel that way too on some level - they just accepted that it was unfeasible to backpedal on something like this post-release, so instead they made the adjustments that SV could actually support. Only time will tell if Indeedee-F keeps the move in later Gens or if they take the opportunity to take it back out when they can wipe transfer moves in Gen X.