Ask eight pilgrims and you will get maybe a dozen opinions. Rucksack volume is a highly personal thing.
My observation, through experience and here in the forum, is that the 'sweet spot" for a man is about 35 to 40 liters. For women the sweet spot is usually about 32 to 38 liters.
Larger than that range, and the excess volume trends to "suck up" extra non-essentials, and weight.
Smaller than that range, and you may have too many dangly bits hanging outside your main compartment where they can be seen, and possibly "borrowed."
I started doing my Caminos with a 48 liter Osprey Kestrel Rucksack, then transitioned to a 38 liter Osprey Kestrel. That works very well for me. However, I am toying with reducing that further to 32 liters. I bought a roll top, dry bag rucksack from Berghaus for that. We will see what happens next Camino season.
In the name of full disclosure, I customarily wear a 'belly bag" holding maybe 10 liters of stuff I must have quick at hand: water, cellphone, guidebook, snacks, buff(s), sun hat, umbrella or poncho, etc. I have rigged this smaller bag to be attached to the front of my rucksack harness. This reduces having to remove the rucksack most of the time.
I have found over the years, that removing my rucksack seems to send send a signal to the rest of my aging body that today's walk is over and it is time to relax. I only remove the rucksack once it is hoisted first thing in the morning if I am going into a cafe or tienda, where it would be inconvenient to others.
What most of us, men and women, discover is that "less is more" on the Camino. Choose items that serve multiple purposes - everything must serve at least two uses to be considered. Any more than three underwear changes (1 worn and 2 being washed and dried) is overkill - except MAYBE in the coldest part of winter.
After lugging extra clothes you did not wear or stuff you over-planned for and did not need, we usually learn. That is one reason why Ivar's side hustle, accepting and storing boxes mailed to him by pilgrims en route to Santiago from multiple directions, is such a worthwhile business. It works for all involved. On some Caminos I have sent him 4-5 boxes of stuff from my Camino. In this regard, I know what I am talking about.
Spain is a modern, first world country. You can buy anything you need along the way. No need to schlep everything from home.
Carefully read everything in this dialog, then use the search function to find other threads on specific issues. Most every question has been asked and answered many times.
Hope this helps - Buen Camino!
Tom