Is there a crypto technoogy that solved the problem of waiting such a long time to be "sure" the transaction is "safe?
It's not a "problem" per se.
It's a feature, not a bug.
Like I said earlier, transaction confirmation/finalisation in POW coins is probabilistic, not deterministic.
Each confirmation increases the probability that a block that includes a transaction will not be overwritten by another due to a double spend, 51% attack or blockchain reorganisation.
Also, when all of the blocks were mined, and miners will have to make a business model based only on transaction fees (currently as I see it it is all/monstly about block reward).... how will the miners pack the transactions
I reckon it will still be the same on the protocol level.
In this case, the Coinbase transaction will only include the transaction fees.
will the "dificulty" be set to a very high number so basically each "try" will generate a new block (he will not get the reward), and the coinbase transaction will only include fees? If this is the way it will happen, then there will be a higher possibility of forking (because every miner would generate a block very quickly) - right?
That's not how mining works.
The difficulty has nothing to do with the block reward but adjusts itself every 2016 blocks to the median hashrate of the network.
Also, not every "try" generates a block, which is why (bitcoin) mining is competitive.
The bitcoin network has a collective hashrate of 24,785,843,885 GigaHashes per second.
1 GH/s = 1 000 000 000 hashes per second
Do the math to see how many trials to create a block goes on in the bitcoin blockchain every second.