how many of you change the spare tyre at regular interval at let's say 3 years once? or pump your spare tyres while you pump the other 4 donut?

i have this spare tyres that staying behind car boot since day 1 the car bought, and hardly pump air in it and today i go and pump the air pressure is almost empty inside i wonder is it safe to be use anymore since the age of tyres is probably 6 years old, even my car tyres also running on the 3rd set now since we bought the car

For my case, i will pump my spare tyre once per month (I also have a battery operated pump in my car boot for emergency situations)

I will recommend you to change your 6 years old spare tyre as the rubber might be harden although it looks good from the outside. Not worth taking the risk.

Next time u change your tires ask the tire shop to swap you old tyre with your spare

problem is the spare tyre is different size, brand and threads so i dont think it is wise to swap, even if same brand also the thread wear level will be different

spare tire is only for emergencies. you wont be driving it much (or fast for that matter). difference in size is ok, though usually spare tires are smaller, i'm not sure if it will be an issue if they are actually bigger
don't think anyone has that issue, since people usually upsize rims, not down size
notice most newer cars today with 16/17" rims, they have 15" steel rims as spare.

Also, can opt to pump more air (35-40 psi?) into the spare tire so you don't have to deal with it too frequently. can then check every few months (maybe 1-2months?) for spare tire condition (if got crack? or if the air pressure is sufficient)