I haven't used this myself, but maybe this?
https://gist.github.com/victornpb/135f5b346dea4decfc8f63ad7d...
Most platforms do not even let you edit or delete messages at all.
Just log press, delete and select "Delete for me and <other(s)>".
In Telegram, as an admin you can also select auto delete for a group.
Discord will ban you for that, even if you delete your messages with the app on a stock Android without any macros or other tools that reduce the required effort over the naive way (e.g. `from: namibj` search; repeat for each "server").
(Btw; you have a pending email. I lost my old domain, but keybase has other accounts and an encryption key linked. You have 24h before I'll have to reach out harder, due to acute urgency.)
Also, Discord might be a "nice" company right now, but maybe it gets bought by facebook in 5 years.