Unfortunately the so called pressure treated timber does not last very long.
The chemicals used are generally dissolved in water and not very effective long term, this applies to fencing, posts, decking and joinery. C
ompounded by the poor quality rapidly grown timber.
I purchased some 200 X 75 timbers, had them cut to length before treatment = full protection ??
I used these as a stand up base for a greenhouse , about 500 mm of one is almost completely rotted away and the bottom’s of the others are well on their way.
There is nothing like the old creosote/ tar oil. Yes I know it is not ecofriendly, neither is petrol and diesel😁