Parkrun (also Parkrun US and the original Parkrun UK) is a fun, low-key, 5k weekly race.
No cost to enter, no awards, and lots of cool results data on their website.
The only thing you need to do is register (free) and bring a barcode to be scanned to record your result.
I don’t like carrying a phone with me when running, so I went looking for an Apple Watch barcode for this. I found https://dfyb.run which is very-well done and works perfectly.