Chaos takes new builds first, sometimes several in a day. Anything here is worth an hour of your time.
Start with what changed last
The patch notes list every change in every build, newest first, with a build range picker. Your build number is on the login screen, in the line at the top left that starts with Chaos Shard. Read the notes from that build back a few, pick the entries that touch how you already play, and go see whether they hold up.
Systems that want eyes
These are on Chaos now and are large enough that ordinary play still finds things in them.
Lot auctions in NPC towns. Bidding, outbid notices, what happens when an auction closes while you are offline, and what the deed does when it arrives.
Free house placement. Move and rotate a house anywhere on its lot, on slopes and against walls, then check that doors, decorations and the entrance still behave.
Player dungeons. Digging, the generator chest, totems and traps, publishing, and whether another player can walk your dungeon the way you meant. There is a full manual for it.
Search all my stuff. Find an item across bank, backpack and houses, and check the counts match what is really there.
The opening for a new character. Make a fresh character and play the first hour the way someone who has never played would. The start was rebuilt and the parts that trip people up are the parts we cannot see from here.
Creature support abilities. Some creatures now buff and heal their allies. Fight kobolds and watch what the casters do to the fight.
Catchphrases. Set phrases on a character and check they fire in the situations you chose, on every character on the account.
Paired dancing and emote copying./partner and /mimic with someone else, across scene changes and while moving.
Reporting what you find
Type /oracle or /ask in game, describe what happened, and it files the report with your name on it. No tester status needed. A report that can be acted on carries the build number, where you were, what you did, what you expected, and what happened instead.
The testing handbook covers the rest, including what tester status adds and how the fix loop works.