Glass joint stuck in flask
You have multiple options.  All of them assume that the distillation setup is empty, at ambient pressure.


Of course, like mentioned in the comment by @Waylander, put a little of (silicon) grease on the glass joints prior to the distillation, just enough that they become transparent.  There are multiple kinds of grease, suitable for different temperatures / pressures during the application.
If grease is not an option, there are sleeves made of PFTE / teflon to be put on the joints.  They are available in different diameters, and forms, e.g.




(source, source)


Especially for vacuum distillations, but not limited to this: the best remedy for this issue is to dismount the distillation right after the recovery of the product fraction(s), while the parts (e.g., column, head) are still considerably warm.  Otherwise, once cooled to rt, the setup then often will stuck much better than ever intended.  Depending on size of the distillation and remaining temperature of these pieces, wearing gloves (to protect your hands against the heat) may be helpful.  Then, it is better to allow the warm pieces to cool to rt while being put e.g. on cork rings.
«Forgotton» and already stuck glass joints may be detached from each other if you immerse them in the basket of a ultrasound bath.  Addition of some of detergent to the water bath helps while occasionally gently pulling the pieces apart.
If you have the dexterity (some develop this over time / by experience), wear both gloves to protect your hands against heat and goggles: you may heat the circumference of the outer wall of the glass joint with a heat blower or even a heat gun / pocket burner.  The aim here is that the outer part of the joint dilates quicker than the inner part.  It is the most risky variant because uneven heating may shatter your distillation into pieces; especially if the parts joined together are made of different types of glass with different expansion coefficients.  It this is not for you, just ask your local glass blower for assistance.