I am working with gnuradio-companion in (End-of-Life) GNU Radio 3.7, working on a bigger project with a lot of blocks for the first time. The space on the workbench is getting scarce.
Do you know if it is possible to increase the size of the workbench?
Starting with GNU Radio 3.8, this is no longer necessary: the canvas auto-adjusts its size, and you can zoom around in it (usually, using ctrl+scroll wheel).
So, if this is a problem you're encountering, you're using the End-Of-Life GNU Radio 3.7 release series (or older). You should not be doing that. It's time to upgrade your GNU Radio.
To preserve the old answer:
Double-Click on the "Options" block and adjust the "Canvas Size" (it's width, height in pixels).
Another good approach to keep your flow graph manageable is to take groups of blocks and put them into "hier" blocks (select connected blocks, right click, more, Create hier); use "Pad Sinks" and "Pad Sources" to create in- and outputs for your new hier block, and use that hier block in place of the bunch of blocks, to keep your flow graph tidy!