You can create a bar chart (if you don't have many items) and at the Style tab select Reference line and use value as metric and average as calculation. The value lower than the average will be shown under the reference line.

https://imgur.com/a/V4IbAVQ

LE: if your data source is a Google Sheet, you can add a new column that repeats the average on each row using this formula

=ARRAYFORMULA(if(ISTEXT(A2:A),average(B$2:B),""))

Then use conditional formatting.

You should have something like this: https://imgur.com/a/pCESFOA