You don't need an app to use Mastodon.
There's an excellent official website interface you can use, it works well on phones, computers and tablets.
The web interface gets all the latest features first.
(Note: in mobile mode the search box is hidden behind the # or ? icon)
To try it out, just go to your server's website and log in with your account.
If you don't know your server's website address, it will be in the last part of your account address (more info: https://fedi.tips/how-to-use-mastodon-and-the-fediverse-basic-tips/#WhatsMyAccountsAddress)