[R-sig-Debian] Configure error: checking if libcurl supports https... no

[Johannes Ranke]

...

> > curl: /usr/local/lib/libcurl.so.4: no version information available

so here we have evidence that indeed you have a locally compiled curl version 
on your system in addition to the Ubuntu one (which would not put anything 
into /usr/local/lib).

So it seems that at some point you have downloaded curl sources and installed 
them into your system, and that this version (as it has no https support) got 
in the way configuring R 4.1.0.

If you still have the sources lying around, there is an uninstall target in 
the Makefile, so you should go to the source directory and do a

sudo make uninstall

to get rid of your local curl version in /usr/local/.

Johannes