devtools problem on MacOS 10.14.6

Hi--- I would like to install the new package lcvplants 
(https://www.nature.com/articles/s41597-020-00702-z.pdf, 
https://idiv-biodiversity.github.io/lcvplants/articles/taxonomic_resolution_using_lcplants.html) 
and need to use devtools to do so.

I don't seem to be able to install devtools:

R version 4.0.3 (2020-10-10) -- "Bunny-Wunnies Freak Out"
Copyright (C) 2020 The R Foundation for Statistical Computing
Platform: x86_64-apple-darwin17.0 (64-bit)

 > install.packages("devtools")
Warning: unable to access index for repository 
http://cran.utstat.utoronto.ca/src/contrib:
 ? cannot open URL 'http://cran.utstat.utoronto.ca/src/contrib/PACKAGES'
Warning: unable to access index for repository 
http://cran.utstat.utoronto.ca/bin/macosx/contrib/4.0:
 ? cannot open URL 
'http://cran.utstat.utoronto.ca/bin/macosx/contrib/4.0/PACKAGES'
Warning message:
package ?devtools? is not available for this version of R

A version of this package for your version of R might be available 
elsewhere,
see the ideas at
https://cran.r-project.org/doc/manuals/r-patched/R-admin.html#Installing-packages 

 >

and same result after updating...
R version 4.0.4 (2021-02-15) -- "Lost Library Book"
Copyright (C) 2021 The R Foundation for Statistical Computing
Platform: x86_64-apple-darwin17.0 (64-bit)

My thanks to anyone who can suggest a way forward!

---tad.

  
<++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
<Tim Dickinson
<Senior Curator Emeritus
<ROM Green Plant Herbarium (TRT)
<
<Department of Natural History
<Royal Ontario Museum
<100 Queen's Park
<Toronto  ON
<CANADA  M5S 2C6
<
<Phone:  (416) 782 1607     FAX:  (416) 586 7921
<E-mail:  tim.dickinson at utoronto.ca  -  ORCID ID http://orcid.org/0000-0003-1366-145X
<URL: http://www.rom.on.ca/en/collections-research/rom-staff/tim-dickinson
<++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++