CW: suicide
Coming from someone who has spent considerable time thinking about and planning suicide by train: lol no
Unless you put up walls higher than the highest ladders available (so at least 5m I guess) or completely enlose every train track with a roof and everything, people will climb over things. There's either no space for large fenced areas around tracks (pretty much everywhere near civilization) or you're too far out for somebody to respond before a determined person can reach the track. And of course, nobody will permit the construction of the necessary infrastructure (call them NIMBYs if you want).
Every escape door can be used to enter tracks. Make them as secure as you want them - keys are easier to get then you think.
Rebuilding train stations to completely secure access to the tracks would involve standardizing all trains in every country in all of Europe.
And (not applicable for high-speed trains) unless you want to spend billions and years to rebuild every train crossing to bridges, it will be impossible to completely secure the tracks.
Most train suicides are impulsive decisions and can be prevented with better infrastructure. But if suicide by train is too difficult, I'll just jump on front of a car instead, or from a bridge, etc. "It's all just a lack of investment" so is terra forming Mars. But spend a fraction of this for better mental health and you can prevent many more suicides.