due to the way the Fediverse works (servers hosted on many different machines rather than one large machine), text search isn't (officially) possible. on Mastodon you have the option of searching by hashtags, but I don't think that works on Lemmy.
you would have to use an external search engine like DuckDuckGo, Google or something like https://www.search-lemmy.com/
No issues with the GPlay version on Android 11