Details at https://twtxt.dev/ and elsewhere. This has been in development since 2016. All you do is create a txt file in www or html and include info like
# nick = username
# url = https://example.com/posts.txt
# avatar = https://example.com/avatar.png
# description = Describe this
to then begin posting using a command like like
echo -e "$(date -u +'%Y-%m-%dT%H:%M:%SZ')\tHello to all of you out there! >> posts.txt
There are various registries and places you can submit your user via curl to become more discoverable by others. Also tons of spin-offs that add support for fancier markdown and such, but haven't tried those yet.