The text height and other size settings for dimensions have to suit to the size of the drawn object, units and intended (printing) scale. So if it's a mechanical part in mm, let's say 250mm long and to be printed in 1:1, the preset values in options - current drawing preferences - dimensions might do it. But if it's a building, in meters, to be printed in scale 1:100, you will have to change these settings. With 'general scale' you can modify all the values (except 'fixed length'), so you don't have to change all the individual values for a different scale. Also ensure a paper size is set.
I had the same problem, finally figured it out but also wasted a lot of time. I've been messing with Librecad for a couple of years and have yet to get it to be useful. I just installed 2.1 (linux) hoping it was fixed, it's different but still not useful. I'm a toolmaker and use CAD every day for the last 30 years so I'm not a newbie but I prefer Linux and wish there was a usable Linux 2D CAD application, Librecad is not it.
The forum is elaborated and commendable. I had this issue a few months ago and it was resolved due to help in this forum. At the moment I have another co-related issue with my antivirus turning off mcafee firewall in windows. Suggestions are welcome.
What is your intended printing scale? General scale set to 0.1 means 10:1 on paper. Meters in 10:1 on A4? You have to use the reciprocal value. As the drawing is scaled down at printing the dimension text must be larger, not smaller.
In 2.2.0 rc also be sure Draft mode is not on, otherwise you get boxes for text.
I had so many problems with LibreCAD using mouse input along with command line inputs that i switched to QCAD also. I have found QCAD to be less problem prone but I still check this forum to keep up with possible improvements as they are made and someday may switch back to libreCAD but for now it's QCAD for me.
I did have to pay for QCAD but it is only a one time charge (you purchase a permanent license) and it was about $35. I also bought the online user manual for $17. I consider it to be well worth the small amount of money.