So that's a mortise lock, used with a skeleton key and should be a simple fix to get the lock working for you. There are 2 types of skeleton keys, just go buy each one at your local hardware store, they're $2 bucks at my Ace hardware (I too have skeleton keys and mortise locks).
Hopefully it's just the paint that has the bolt stuck inside the panel. You have to remove the 2 screws on that side panel. Remove panel. See if the paint can be scraped away from the deadbolt. It 'may' work if the paint is what's keeping the bolt stuck inside.
And if it's not the paint, it's a simple fix to fix mortise locks.
Here's a quick video and a list showing different mortise locks, it may help you narrow down which one you have, although you don't really need it to fix your lock, it may just help you to familiarize yourself with the inner mechanisms, this making it a bit easier to understand what ya need to do.
(If you put a skeleton key inside and turn it to locked while you're in your bedroom, nobody can put a key in the other side to open your door while you occupy it (when you are sleeping, for instance).
https://www.historichouseparts.com/antique-mortise-lock-resources.html
If this is too much, the easier way is the outside clamp on door lock, $20 bucks on Amazon.
Door Handle Lock, Door Knob Lock Out Device,Cover to Disable The Doorknob/Faucet/Valve, Prevents Turning of Door Knob and Access to Keyhole, Prevents Operating The Knob
https://www.amazon.com/Disable-Doorknob-Prevents-Operating-Password/dp/B09XXBG7CP
Hope this helps and you can get the peace of mind and security deserved 😉