Well well well, this is basically the inverse question to "Yes but can we make Venus spin ?"
The answer of course being, yes.
To add some context, the Angular Momentum of any planet is not actually that much. For example, if you wanted to spin up Venus to a 24 hr day night cycle, that would requiere about $1.88e29$ Joule of Energy. Now that sounds like a lot, because it is. But it also really isnt. Its the kind of Energy you can reasonable produce in a given period of time. For Venus, if you install 1400 Mass Drivers firing 100 Ton projectiles every 84 Minutes (So the Mass Drivers fire continously but each individual one only every 84 min), it would only take 300 Years to spin the planet fully up.
Now, the reason it would still take so long is because Planets are not solid. You need to apply a constant force over a long time, otherwise the Planet will absorb the energy. Hence why Tidallocking usually takes millions of years to happen. The Tidal Forces are not large to beginn with and they are not as constant as you would like. As the Orbital distance changes.
This is also why you cant just snap your fingers and make a planet spin or slow down. Even though the Rotational Energy of a planet (All things considered) is not super big, the Inertia is absolutly massiv. And if you dont apply this force evenly everywhere, the planet will turn into lava. It wont blow apart or anything, but the Energy will vaporise everything on the Surface due to friction.
So, for your planet there are 2 ways to get Tidal Locking which dont evolve Magic or Technology.
Either, the Planet never rotated that fast to beginn with and just came to a halt when a Civilisation arose. This might be your best option because if the Planet becomes tidally locked it will lose its Magnetosphere. Same the other way around btw, if we Spin up Venus she will regain her Magnetosphere as we are literally restarting geological processes. Meaning, your mass extinction could be in part duo to the planet losing its Magnetosphere. Which in combination with the heat, shutdown of major Geological activity etc might very well be enough for a Mass Extinction.
The other option is significantly more violent. In theory, your very unlucky planet could interact with another major planetary body. A body which cancels out the Angular Momentum over a given period of time.
Needless to say, this is very unlikley but it gives you a bit more freedome in the timeline. But it would also probably kill every lifeform on the planet.
For the most part, these are your two Natrual options. Again Magic can do anything and there are technological ways that can slow the planet down significantly faster. But it really depends what your precise goal is. if you want a story where you explore the impacts of a planet suddenly stopping, well then Magic is your only real option. If you on the other hand want to explore how Evolution and slow processes adapt to this new Enviorment, you can just say the planet became locked from the Star.