Could you please explain me whether there is an arbitrage opportunity in this situation (added below)?
On an expiration basis, your put protected long underlying makes money above $80 and you have a locked in loss of \$5 below \$75.
Note that long underlying plus long put is synthetically equal to a long call. Pretending no carry cost or dividend, your position is the same as buying the \$75 call for \$5 and the P&L is the same as stated above.
There's no arbitrage.