I'm a senior engineer but I miss just writing code, what now?

You have reached the senior level, and with it came system design and mentoring and meetings, while the simple joy you loved, being handed a problem and solving it, has thinned out. That grief is real. You did not fall out of love with the work. The work around you changed shape. Growing did not erase the coder in you. The pleasure of solving a clean problem is still available, it just does not fill your whole day anymore. Part of maturing is finding meaning in the new parts too, the quiet satisfaction of a junior you mentored writing better code because of you. That is its own kind of solving. You can also protect what you love on purpose. Keep one hands-on problem for yourself. Take a thorny technical piece now and then instead of handing it all away. Nobody says a senior must stop coding entirely. Design your role so it still holds the thing that drew you here.