"If a foreign investor can be present in the country, why are there various obstacles that our own people cannot enter the field of cryptocurrency mining?"
the answer is simple.
the 'investor' uses the industrial capacity. that can actually cope with high MW electric.
home hobbiests in iran will not get 3.25kw from their house wallsocket. so need to fiddle with their circuit breaker.
these things cause neighbourhood power cuts as its too much for residential capacitors
imagine a street of 10 houses. each with a 4kw capacitor. but each house only uses say 1kwh
the street can supply 40kwh but is only utilising ~10 normally
suddenly turning on just one s19 makes that street need to suddenly demand a 14kwh supply. which if the network is not set up means there can be some brownouts (dimming lights)
if the residential hobby miner has more asics running. it can get worse.
if there was someone with say 9 asics (29.25kwh) then if one of the houses suddenly wanted to boil some water whilst watching tv. that puts the whole street over the 40kwh limit for their usual household and asic draw.. causing a circuit break.. aka power outage
home users fiddling with their circuits to get more then 4kwh from within their property can cause issues not just for themselves. but their neighbours too