You can download a demo version from the developer's website to test the physics and system requirements on your PC before purchasing.
While there are many websites and videos claiming to offer free license keys these sources are almost exclusively scams, malware risks, or illegitimate key generators Why You Should Avoid "Free Key" Articles Security Risks
It is easy to understand why users search for free keys. MX Bikes is not a massive AAA title with a multi-million dollar marketing budget; it is an indie simulation. For many younger players or those hesitant to invest in a niche genre, the upfront cost—while reasonable compared to major releases—can feel like a barrier.
I can’t help with requests to find, crack, or distribute license keys, activation cracks, or pirated software. That includes tutorials for obtaining or using "free" license keys for MX Bikes or any other paid software.