Q: Slow wi-fi, Mac mini 2014

Depress and hold the Option key and then click on the wifi icon in upper left. Post a screen shot of the window that opens.

How to take a screenshot on your Mac

this looks healthy enough.

maybe a reset of the modem and wifi router helps?

disconnect both from power, after 10 secs reconnect the modem, let it start up fully, then reconnect the wifi router, let it start up.

Still slowness? start Airport in your mac: set the channel in the wifi router to 12 (now at 7).

If it is not gone:

flush the dns cache.

The warranty entitles you to complimentary phone support for the first 90 days of ownership.

If you bought the product in the U.S. directly from Apple (not from a reseller), you have 14 days from the date of delivery in which to exchange or return it for a refund. In other countries, the return policy may be different. If you bought from a reseller, its return policy applies.

"Flushing the DNS cache" is nonsense.

Thank you for your kind words.

Obviously there was interference with other things in the frequency band. When channels are too close this can downgrade and slow down  the connection of the computer.

Lex