bitcoin-qt sync issues and slow speeds

I've got bitcoin-qt up and running, trying to grab the whole blockchain which is around 600GB now. Feels like just yesterday it was about 250GB, but that was like 4-5 years back. Now, the syncing process is dragging way more than it used to, and I'm wondering why. A lot of the time, I notice I have just 1 peer or none at all. Overnight, I managed to download maybe 2GB. The peers chart hardly shows any activity, just a few spikes here and there, nothing steady. I checked with iotop, and it says bitcoin-qt is reading and writing a few megabytes per second, though. I'm at 97% complete now, so I guess I'm downloading blocks that most folks already have. What could be causing this irregular and slow download speed?

How much memory do you have? Do you have an HDD or SSD? Obviously, syncing will happen faster on a SSD than an HDD. With that being said, blocks from around the 97th percentile (or anything mined one year ago) are plagued with Ordinals transactions which are really heavy and take a long time to process, so that is probably the reason why verification has slowed down. You can use the addnode RPC call to add some other peers if it's not connecting to any for some reason.

it's more likely possible that due to the limited number of peers paring the transmission is slow, there is also a possibility of a bandwidth issue with the peers, many other factors can affect speed as NotATether  mentioned your disk I/O also holds a significant role.

I have a 2TB HDD (circa ~2017) and a Core i5 4th gen (current generation being 14). I've used various Internet connections, some fast, some slow. I typically run it overnight. I did a partial sync of just the first 250GB, maybe a year ago, I was using a Raspberry Pi 4 and my old circa-2010 250 GB SSD, and a 200mbs Spectrum connection. That went pretty quick. The original time when I synced the full blockchain was at the beginning of the pandemic and it went very fast over LTE. During the pandemic my phone carrier gave my $30/month connection unlimited hotspot data. I was using the HDD then and a Core i5 5th gen. If I use addnode RPC, whose server would I be adding? Is there a risk that Ordinals might burden the blockchain and make it unusable?

The easiest way to do is upgrade your RAM. If you can afford to have a SSD, let's upgrade. Check this tutorial to download Bitcoin Core too. Sharing for Bitcoin Core download: the cheapest pay-per-hour VPS I found.

It's known Rasperrby Pi 4 (even you own 8GB ones) struggle to sync not only due to somewhat slow CPU, but also due to total UTXO above RAM size. Although if you haven't allocate Bitcoin Core to use most RAM, you can by do that by editing bitcoin.conf and add line dbcache=X where X is RAM which used by Bitcoin in MB. You can't really upgrade RAM capacity of Raspberry PPi 4, unless you're willing doing it the hard way[1]. [1] https://hackaday.com/2023/03/05/upgrade-ram-on-your-pi-4-the-fun-way/

Any chance you have a firewall, modem or ISP that's blocking connections? That's normal, especially when you're low on RAM. I counted several TB read/writes in total just to sync Bitcoin Core with 8 GB RAM.