

I know you mentioned Nextcloud and if you happen to already be running it you can use the add-on/module/whatever called Secrets, its exactly what you describe. You make note, send link (can password protect if you want) and once its been viewed its gone.
If you don’t already have Nextcloud, check out vaultwarden’s (bitwarden) send feature.
Or they just call it a under documented or undocumented feature (thinking specifically about the Azure feature to let you access other tenants if they are using that Tenable reported last June).