If a #hashtag doesn't show up when you search for it like #FLE on http://mastodon.social/

you can always use the url shortcut as follows:

mastodon.social/web/timelines/tag/FLE

https://mastodon.social/web/timelines/tag/FLE

toot ! 🐘

#Mastodon #hashtag #search #problem
#Matodon #nimi_lukin #lukin #pakala #sona

Like you can see on this picture, on http://mastodon.social/ , you get five suggestions but the existing #FLE isn't part of them: https://mastodon.expert/media/Yy2Ske6fuOuqUpQr59I