For food crops you can still do pretty well on a 100 acre farm. Berries/fruits/vegetables/etc. Especially if you live in a community with access to distribution for said crops.
I live in an area with a lot of food ag and it's not uncommon for farms of just a couple dozen acres to pay the bills.
This metric is misleading because of how it's calculated. Since you're weighting each farm equally, a 1M acre farm gets the same amount of weight as a 100 acre farm. Therefore, if in a country you have 100 acres of farmland in total, and the farm sizes are 90, 2, 1, 1, 1, 1, 1, 1, 1, 1, you'd end up with an "average" farm size of 10, but in reality most of the farmland is actually part of a megafarm.
While, farm consolidation is a growing concern (pun very much intended), the current reality is that large mega-farms are still the minority. Family owned farms still account for 89% of all agricultural product in the US. 47% of production is coming from farms grossing less than $1 million annually.
Sources: https://www.ers.usda.gov/data-products/ag-and-food-statistic... https://www.usfarmdata.com/percentage-of-small-medium-and-la...
There are also a lot of small farms that are run by teachers (works well with the summers off).
But I think you would find that anything over 50 acres in an area with distribution options (either close to a packer for that product or urban area) CAN be a full time job if you know what you are doing and are willing to work that hard.
The neighbor across the street farms 400 acres of crops. The average farm on their street is 134 acres. The first two families don't even consider themselves farmers.