Updating RVM, Ruby, and Rails on macOS

I'm using macOS in development (Ubuntu in prod), and want to update things for my next project. But I keep running into issues:

$ rvm -v
rvm 1.28.0 (latest) by Wayne E. Seguin <wayneeseguin@gmail.com>, Michal Papis <mpapis@gmail.com> [https://rvm.io/]

$ ruby -v
ruby 2.4.0p0 (2016-12-24 revision 57164) [x86_64-darwin16]

$ brew -v
Homebrew 2.4.9
Homebrew/homebrew-core (git revision 50be1b; last commit 2020-08-08)
Homebrew/homebrew-cask (git revision ccae745; last commit 2020-08-08)

$ rails -v
Rails 5.1.6.1

if I turn on auto-update rvm

I cannot get past the first step in updating rvm

$ rvm install 2.6.1
Found old RVM 1.28.0 - updating.
Downloading https://get.rvm.io
Downloading https://raw.githubusercontent.com/rvm/rvm/master/binscripts/rvm-installer.asc
Verifying /Users/edmund/.rvm/archives/rvm-installer.asc
gpg: Signature made Wed Jul 24 05:59:45 2019 HKT using RSA key ID 39499BDB
gpg: Can't check signature: No public key
Warning, RVM 1.26.0 introduces signed releases and automated check of signatures when GPG software found.
Assuming you trust Michal Papis import the mpapis public key (downloading the signatures).

GPG signature verification failed for '/Users/edmund/.rvm/archives/rvm-installer' - 'https://raw.githubusercontent.com/rvm/rvm/master/binscripts/rvm-installer.asc'!
try downloading the signatures:

    gpg2 --keyserver hkp://keys.gnupg.net --recv-keys 409B6B1796C275462A1703113804BB82D39DC0E3

or if it fails:

    command curl -sSL https://rvm.io/mpapis.asc | gpg2 --import -

the key can be compared with:

    https://rvm.io/mpapis.asc
    https://keybase.io/mpapis

And when I follow instructions:

$ gpg2 --keyserver hkp://keys.gnupg.net --recv-keys 409B6B1796C275462A1703113804BB82D39DC0E3
gpg: requesting key D39DC0E3 from hkp server keys.gnupg.net
gpg: unable to execute program `/usr/local/Cellar/gnupg2/2.0.30_3/libexec/gpg2keys_curl': No such file or directory
gpg: no handler for keyserver scheme `hkp'
gpg: keyserver receive failed: Keyserver error

following the "if it fails" instruction doesn't seem to raise errors but do not help the problem

command curl -sSL https://rvm.io/mpapis.asc | gpg2 --import -
gpg: key D39DC0E3: "Michal Papis (RVM signing) <mpapis@gmail.com>" not changed
gpg: Total number processed: 1
gpg:              unchanged: 1

Am I missing something obvious?

If I turn off auto-update rvm

$ rvm install 2.6.1
Warning, new version of rvm available '1.29.10-next', you are using older version '1.28.0'.
You can disable this warning with:    echo rvm_autoupdate_flag=0 >> ~/.rvmrc
You can enable  auto-update  with:    echo rvm_autoupdate_flag=2 >> ~/.rvmrc
Searching for binary rubies, this might take some time.
Found remote file https://rubies.travis-ci.org/osx/10.15/x86_64/ruby-2.6.1.tar.bz2
Checking requirements for osx.
Installing requirements for osx.
Updating system....
Installing required custom packages: homebrew/dupes homebrew/dupes.
Error running 'requirements_osx_brew_install_custom homebrew/dupes homebrew/dupes',
showing last 15 lines of /Users/edmund/.rvm/log/1596893890_ruby-2.6.1/install_custom.log
    do
        brew tap "${__tap}" || return $?;
    done
}
current path: /Users/edmund/Documents/playground/ugdev
GEM_HOME=/Users/edmund/.rvm/gems/ruby-2.4.0
PATH=/Users/edmund/.rvm/gems/ruby-2.4.0/bin:/Users/edmund/.rvm/gems/ruby-2.4.0@global/bin:/Users/edmund/.rvm/rubies/ruby-2.4.0/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/opt/X11/bin:/Users/edmund/.rvm/bin
GEM_PATH=/Users/edmund/.rvm/gems/ruby-2.4.0:/Users/edmund/.rvm/gems/ruby-2.4.0@global
command(3): requirements_osx_brew_install_custom homebrew/dupes homebrew/dupes
++ typeset __tap
++ for __tap in '"$@"'
++ brew tap homebrew/dupes
Updating Homebrew...
Error: homebrew/dupes was deprecated. This tap is now empty as all its formulae were migrated.
++ return 1
Requirements installation failed with status: 1.

Already updated brew by the way...

Any clues?