If I select text in a text box, then change the value in the Font Size box to, say, 43 - which is not a value accessible in the drop-down menu of preselected font sizes, nothing happens.

Describe your OS & version, the version of Inkscape and the installer you used, plus any special hardware like tablet/stylus or multiple monitors.

Sure thing,

macOS 10.13.16 High Sierra
Inkscape 1.0.1 (c497b03c, 2020-09-10)
Mac Mini and USB Apple keyboard, no tablet/stylus
Monitor Benq GL2460

Seems to work as expected in Linux and Windows.

Info on searching the bug reports and adding new reports: https://inkscape.org/forums/beyond/how-to-report-bugs-or-request-new-features/

99% of the problems I have "seem to work fine on Linux and Windows"... Linux has a 2% market share while macOS has 10%... And most designers in the world use macOS... maybe the developers of Inkscape should have more mac users in their dev/review team? Is there a page to make that suggestion to them?

The bug seems to have been listed over 6 months ago... https://gitlab.com/inkscape/inbox/-/issues/3233

It is not clear from your description if you are entering a number in the Text tool controls, or in the Text/Font dialog. I presumed in the controls.

Apologies for not describing it well enough. Didn't realize there were two different boxes for font size.