for client, I suggest moshidon (forked from megalodon) it foss and available in f-droid

• can add other instances in seperate timeline
• material 3
• full based functions

If you not use English speech, try to find your local language. or just use popular instance (i.e mstdn.social mastodon.social) select with:

• instance server rules that you agreed
• server never down before

TL;DR I suggest to use official instance cuz it has many people in local instance