Horde is absolutely viable! It’s a bit quieter than the Alliance but I feel the community is closer and geeeenerally speaking the quality of RP is higher (excepting a few individuals like myself).
I may be an Alliance KING nowadays, but as someone who lead a Horde guild beforehand (and not too long ago, relatively speaking - it was during BfA) for about a year and a half, maybe a little more, there is absolutely plenty of roleplay on Horde. The faction divide weighs more heavily to the Alliance, yes, but both sides have ample opportunity for it, so don’t feel disheartened and jump in Maalzul . . .
The Horde side is doing relatively good, despite the divide and “bubble communities”. It’s small, but hey - quality over quantity am I right? There isn’t much random/walk-up rp, because it is revolving around events hosted by guilds. Which can be quite challenging for a newcomer.
Obviously you want to figure out what kind of rp you are seeking. Even though the selection of guilds is admirable, at your first steps you can be blind to power-hungry, drama thirsty and even elitist ones. These guilds don’t care about you as a player behind their character, but rather as an addition to their roster, nothing more. That is my experience, but I am sure some others have seen that too.
My advice? Look around, you can still attend to events even wihtout being part of a guild! It requires some patience, but usually it’s rewarded.
For the Horde!
If you’re going to roleplay as Horde here your best option is to find a guild that suits a theme you want. There’s plenty of active guilds around, actual random roleplay outside of that is hit and miss in my opinion. It’s not great on Alliance either but Horde players that go solo are basically relegated to one part of Orgrimmar where the quality of the RP and availability varies wildly. You don’t want to be someone that has to rely on that or hopping from event to event trying to make connections with pre-established friend groups that more often than not are lukewarm when outsiders try to join in.