Garage door posting issue- hello, the door posting of my garage see to have gone rotten/or eaten by rat? at the bottom, with a 2-3cm gap above the ground. What would you suggest to do/fix/repair？ Thanks a lot

Quite normal for timber that meets the ground, normally the bottom section is replaced with a scarf joint (angled cut) it may be difficult to cut out the rotten section because of the garage door mechanism.

As @joe90 says, what you do may depend on whether the mechanism extends down that far and is fixed to that part. If it is not, how about trying to get hold of some 'plastic lumber' (think some park bench seats) and scarfing that in? Wood-rot problem gone, and I for one will probably be dead before the 'plastic weevils' (take that either way) have done their stufff.