[ainarssems]

It's not a good idea to leave car unused for that long parked outside. I would say 3 months maximum without driving if parked outside. Oil that protects metal parts can start breaking down an corrosion can start on things like shock absorbed rods or engine valves. Rubber parts also don't like being left without use for long time. And I am not even talking about things like brake discs or tyres becoming 'square' and vibrating when you start using it again. Starting car for a short while and just idling it to charge battery can definitely be bad for cats and lambdas but it will get the oil flowing around in engine and if you let it warm up and then give it some throttle and keep 2-3k rpm for 5-10 minutes that should clear cats as well. Driving up and down the kerb or even over some wooded planks on the drive if no tax/insurance to go on road will give some exercise to shocks and coat them with a fresh layer of oil.

There are plenty of examples where cars have been standing for longer and are still fine so it depends on individual circumstances.

My neighbour had Astra without use for about 1.5 years and gave it to young relative who was studying to be mechanic as a project. The brakes were seized, brake lines corroded, and engine rusted, no compression and not starting, interior full of mould. He spent way more money on it than it was worth but still could not pass emissions on MOT and finally scrapped car in the end.