WiiM Mini has been pre-calibrated based on the HomePod from Apple's recommendation for AirPlay 2 sync by connecting a zero audio latency based monitor speaker. However, you may connect Mini with a DAC, AMP or powered speaker that has the audio path latency of greater than 0 ms. How you can make it synced with other HomePod or AirPlay 2 speakers like Sonos speakers? You can manually adjust the audio path latency to make it well synced.
How to adjust?
You can use the manual latency adjustment. On the WiiM home App, please select the device tab > tap the device setting gear icon > select sync audio > select manual latency adjustment and follow the instruction on the app to adjust.
If the Mini is slower/later than other devices, you can increase the audio path latency (a bit against intuition) that tells the sync protocol that your speaker has larger audio latency so they can output audio earlier so it can catch up. The rule of thumb is if you're slower than other device, you can increase the audio path delay until you match the counterpart.
Another rule of thumb is that the Aux-out latency is usually less than 5 ms. The optical out latency is usually larger than 10 ms and needs a little bit more time to adjust.