Septic tank pumped 6 months ago, filter cleaned 2 weeks ago, toilet backing up again. Plumbing or septic problem?
With a freshly pumped tank and cleaned filter your next possibility is a flooded drain field
OR
a broken /collapsed or line full of tree roots on the line out of the tank to the field.
I have seen broken lines several times after heavy rains that may have slightly lifted plastic tanks (I have never seen this with a concrete tank).
I would be looking for water to be bubbling if a break, at the break or collapsed line.
If the line is blocked or field flooded the water will make it out to the surface at the tank in most cases where the tank was opened.
If the house is not elevated much (slab) a slow drain field can cause this after heavy rains. I would not expect a 10 year old field to be plugged unless a garbage disposal was used then quite possibly the field could be plugged up.
Standing water at the drain field location may explain your problem if recent heavy rains and after a few days to dry out the ground won’t be saturated and the system will start working again.
Trees in the area could be blocking the flow I have seen willows almost 100’ away plug a drain field the willow was large. Also cottonwood within 50’ and many other trees and bushes closer cause drain field problems. Digging down is sometimes the only way to find the problem if no water is bubbling up.