Sounds like you were sold a pup, but this is firmly in your hands. You're in a (relatively) fortunate position:
Your daily work is so easy it's actually boring, you say. Plenty of time, then, to try little POCs in other languages, to do some self study on the internet, or to perhaps involve yourself in client-facing meetings or other aspects of the company's work, if that sounds appealing. Use the slack to broaden your skills.
An easy job means you leave on time. Go home, do some exercise, eat a healthy meal, then spend a few hours each evening working on personal projects in a much more exciting stack. Instant energy.
You can spend part of your work day thinking about you side projects as well, maybe researching whatever technique or library you need next (but be careful not to do any actual work - your contract likely forbids this).
And spend some time looking for a new job too of course.