1. add mostr relays to your client ( available on https://mostr.pub/)

2. go to https://mostr.pub/ , input the lemmy community, example : @anime@lemmy.ml

3. copy the public key, now type your post in this format : Title Body (can also contain link) @public_key_you_copied

4. post and done ! I have only tested this on amethyst (android) and iris.to (web); unsuccessfull on primal and coracle

check this note as example, note id : nostr:nevent1qqstev94wkdrhyw07chkgy3frf0x3l5n52guzk8x4nd7vp6yak9k56cpr3mhxue69uhkummnw3ezucnfw33k76twv4ezuum0vd5kzmqzypx64xxpmt9xqj3eajy09er38h336xyfmqw3qgva2qlr4e3qt5q2vqcyqqqqqqg54rzcs

if you get it working on any other app, I want to know, I am not really sure what causes this, because it tried to post on guppe groups and chirp.social groups and it did not work !