これは1設定したら不要な気もしますが、何か alias tmux='tmux -u -2' としてました（試行錯誤した跡かも）
-u Write UTF-8 output to the terminal even if the first environment variable of LC_ALL, LC_CTYPE, or LANG that is set does not contain "UTF-8" or "UTF8".
-2 Force tmux to assume the terminal supports 256 colours.
❯ asdf install nodejs 12.14.1
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 3684 0 3684 0 0 48473 0 --:--:-- --:--:-- --:--:-- 48473
Authenticity of checksum file can not be assured! Please be sure to check the README of asdf-nodejs in case you did not yet bootstrap trust. If you already did that then that is the point to become SUSPICIOUS! There must be a reason why this is failing. If you are installing an older NodeJS version you might need to import OpenPGP keys of previous release managers. Exiting.