Git version v2.34.1 on your Linux x86_64 system. The latest version available is v2.43.0. 

##------------
git config --global http.version HTTP/1.1
##------------
git config --global http.postBuffer 524288000

$GIT_TRACE=2 GIT_CURL_VERBOSE=1 git clone <url>

$GIT_SSH_COMMAND="ssh -vvv" git clone <git@url>

$GIT_TRACE=2 GIT_CURL_VERBOSE=1 git clone https://github.com/OSGeo/PROJ.git PROJ_github


##---------------------------------------
##  this variation failed to force 1.1?
# export GIT_HTTP_VERSION=1.1
# GIT_TRACE=2 GIT_CURL_VERBOSE=1 git clone https://github.com/OSGeo/PROJ.git PROJ_github

##------
git clone --single-branch --branch master --depth 1 https://github.com/OSGeo/PROJ
#----

##-- list all configs
$ git config --global --get-regexp . | sort -u

##-------------------------------------------------------------------
## Method to pass a public key w/o  $ssh-agent

user@a30:~$ git clone git@github_key:OSGeo/PROJ.git

##-----------
##  add this 
~/.ssh/config

Host github_key
  Hostname  github.com
  IdentityFile  "/home/user/.ssh/id_ecdsa"