I have a Blogger site. I have configured AdSense in Earnings tab with a valid AdSense account (it has been run for 8 years) but the ads are not showing.
What else can I configure?
It appears here. There may have been a glitch or they may have run out of relevant ads temporarily which target the location you are checking with. Given your site has so little text, it is highly likely since Google prefers not showing ads to showing irrelevant ones.
You can configure the back-fill to serve PSAs. In any case, those do not give any revenue.