What can I do to fix this Bitcoin Core error?

So, I’ve got Bitcoin Core running on a MacOS VM in UTM, and out of nowhere, I got hit with this error message: https://ibb.co/mygtrBH

"Error loading block database" means just that. Have a look at debug.log to see if there's anything useful in there.

Most of the time, rebuilding the blockchain is inevitable. I would just click "OK" and let it do its work. BTW, do you run a pruned node or a full node?

Follow-up question: why do you run a node inside a VM? I can think of a few reasons, but I can think of more reasons to run it normally.

We need more ifnration. Aside from whatever been asked, 1. Do you mean https://mac.getutm.app/ when you say UTM? 2. While i'm not familiar with UTM, on where do you store Bitcoin Core files? Inside one of disk image file? Using mounted folder/disk to the VM?

Pruned. I was running inside a VM because I was downloading some experimental software that required Bitcoin Core to be running in the background. Do you think if I was running a full node that this wouldn't have happened? This was my VM https://mac.getutm.app/ I believe the files are stored here: '/Users/a1/Library/Application Support/Bitcoin'

Hmm let's take it step by step. 1. Pruned or not, doesn't really matter. In both setups, there can be issues like that. 2. I wouldn't run Bitcoin Core in a VM, since there are executables for every OS. Bitcoin Core can definitely run in the background. In fact, if you start it and don't turn the PC off, it will keep running forever. A bitcoin node (computer that runs Bitcoin Core), is primarily used a server that stays online 24/7. It's still unclear why you chose a VM. Did anyone tell you to do so?

Was the VM's storage large enough or did even your pruned node fill up your virtual disk? Filling up the disk could easily corrupt the block storage of Bitcoin Core. Don't forget that e.g. chainstate eats up 12GiB alone in any case. Here's current space consumption of a full node on Linux (without wallets), output of du -h: The VM has to share the ressources of your host system. Host and guest OS have to share RAM and other ressources, so running the node natively could be less ressource-hungry. But sandboxing shady software in a VM is totally legit if you know what you're doing.

Pinpointing the cause requires you to check the "debug.log" file contents in our bitcoin datadir for the related error. Most of the time, it's caused by abrupt shutdown of your VM while Core is still running in the background specially when its dumping data to disk. It would also be beneficial if you tell the name of the "experimental software" since most of those require the whole Bitcoin blockchain intact in disk. It will be a waste if you resync your node while the software isn't compatible with pruned blockchain. On a side note; Bitcoin Core with pruned or complete blockchain are both full nodes since both verify the entire blockchain.