Yes I started having this exact same issue within the last couple days too! It makes it very very frustrating to play the game. It happens for me on Retail where I have a multitude of addons but it also happens on the PTR client where I use very few addons.
The only way to very temporarily fix it is to completely exit the game and restart the game. But it can happen again so easily when you use your mouse to turn your character.
It would be good to consolidate all the reports. As you said there’s a thread on the US forums with the same reports: https://us.forums.blizzard.com/en/wow/t/mouse-turning-into-4-way-arrow-on-right-click/1541149
And here on the EU forums there’s a thread about this issue having started in the Wrath Classic client too: Mouse (left and right) movement behaviour (Wotlk Classic)
On Reddit someone suggested to try the scan and repair option. I don’t know if that’ll help (running the repair as I type this) but it’s worth trying.
Edit: within 5 minutes of playing after running scan and repair the issue occurred again. It did diddly squat to resolve the issue