I am a proof of work believer, because it garanties decentralization on the hardware level (layer 1).
This is not inherently the case in PoS because its consensus algorithm is not dependant on any scarce real world ressource, provided it does not require a huge amount of memory to run a full node.
In this case I would expect that with a decent amount of miners, a PoS network should still be very decentralized, because it would be very unlikely that coincidentally all miners were geografically colocated.
This assumes that the protocol would not support delegated PoS because there it is obvious that it is more centralized.

So what then is the drawback of PoS or is there something that I miss?

In my opinion there is only one way to stop the war in Ukrain immediately and effectively.
Ukraine should surrender to the Russians, but demand from the West that they pledge for sanctions agains Russia until they release Ukraine into freedom.

I want to make a bitcoin transaction, but if it does not make it into the blockchain before a certain blockheight, I want the transaction to expire so that it can no longer be inserted into the blockchain. Is this possible?

As a layer 2 developer of Bitcoin I deem this capability very important and useful.

In the Bitcoin Core source code https://github.com/bitcoin/bitcoin/blob/21ee676dd6a7d9704367b6412bf8e1e443ec2b5b/src/chainparams.cpp#L139 I see that the latest checkpoint is at height 295000.
If I understand correctly, this means that today a miner could produce a block with height 295001. Although this block would not go into the main chain of course it still has to be validated by all nodes, and if valid, it would go into the secondary chain pool.
My question is, how is this block validated, since it is not known anymore what the state of the UTXO set was at height 295000. My guess is that in order to validate, the node has to temporarily reorganize the UTXO set to height 295000, check if block 295001 is valid, if yes store it, otherwise reject it, and then restore the current state of the UTXO.
 
Looks like a lot of work. Is that the way it works?

As I understand, hashgraph does a virtual vote on nodes. So an attacker might set up millions of nodes to outvote the honest ones.
How does hashgraph prevent that?

In https://en.bitcoin.it/wiki/Protocol_documentation#version it says about the nonce in the version message:

Node random nonce, randomly generated every time a version packet is sent. This nonce is used to detect connections to self.

I need some clarification. First, why do I need a nonce to detect a connection to myself, do I not just see that from the IP address? Second, why do I need to create a new nonce for EVERY version message? Can I not just always use the same nonce since this would still allow me to detect a connection to myself.