Hi, nubee to Inkscape and the forum, but I think I stumbled onto a method here.
Using the pen

click once, hen holding CTRL to constrain, draw a horizontal line to the right, and click.
Then using CTRL, move the mouse down to the right at a 45 degree angle. Dont click yet!
Let go of CTRL, and position the cursor directly over the end of the line.
Now click and drag down, then add CTRL to constrain to vertical.
Keep dragging until the handle of the node is at the same height as the horizontal line.
Click, done!
Sounds like a lot, but not so tough once you do it a few times. You can do it without using CTRL, but with it I can make make nice 90 degree turns. It doesn’t make perfectly circular radiuses, but comes pretty close when the angle is a 45.