Anxious about accommodation Sarria to Santiago de compostela

There are many pilgrims that say the albergues fill up quickly, there are equally many pilgrims that say that they always found a bed. Have a look at https://oficinadelperegrino.com
Every evening around 22:00 the office posts how many pilgrims have arrived that day (ignore the current value, it is off, yesterday arrived ~1100 pilgrims if I remember right). Some of them will belong to big groups that sleep in alternative accommodation, meaning not in normal albergues.
I wouldn't worry to much if I were in your place, numbers are slowly going down.
Buen Camino, SY

There are beds. Stop in the early afternoon for the best choice. Santiago is well booked for the popular places. Still there are beds and rooms. While taking the bus to the airport, I counted 150 pilgrims between San Lazaro and Monte do Gozo, a distance of less than a kilometer.

Book the first night, just to have peace in mind. On the spot, and talking with hospitaleros about the situation, you can (or not) make reservations on a daily basis, every afternoon.
In Sarria, I liked albergue Monasterio de la Magdalena: quiet (not in the main street, but close), in a historic building, friendly clerks, roomy, clean, great kitchen.