Yes, they are now marked as spam.

As I am the sole person to ever use this server and I have been sending to some of those emails since almost as long as gmail has even existed, the fact that they are now marked spam is simply an admission that Google doesn't actually give one shit about accuracy and solely trains their ML networks on things that bring them revenue.

Has your IP changed during that time? How do you have SPF and DKIM configured?

These questions don't help. I get that you're trying to troubleshoot the OPs mail server and are trying to figure out what might be done to get their mail delivered again. But that's a form of victim blaming if that server was never used to send spam and the OP is not sending out spam their mail should not be classified as spam and if it is that is clearly uncompetitive behavior by Google because the difference between incompetence and malice is something for Google to illustrate, not for the rest of the world to bend over backwards to accommodate their demands.

Imagine for the moment that the OP's IP address has changed during this time and they don't have SPF or DKIM configured. Or imagine SPF is misconfigured to say "only IP 1.2.3.4 is qualified to send email for this domain" but they've since moved to another IP. Or imagine their DKIM configuration is broken and their messages aren't validating. There are a ton of ways you can configure a mall server so that recipients can't reliably tell you're not sending spam: it's not just what content you send but also the reputation of your IP and the signals you choose to send via SPF and DKIM.

This isn't specific to Google: all the companies that receive email have the same difficult problem. Email is the only major fully open federated push protocol, and spam has come close to killing it.

(Disclosure: I work for Google, nothing related to mail, speaking only for myself.)

One of major advantages of GMail is lack of SPAM and phishing.

If the trade-off is that Google accommodates mails sent from badly configured servers and I receive a lot of SPAM, or they drop that mails and limit SPAM, I will go with less SPAM. I know it's not cool for decentralized Internet, but that's the utilitarian reality for me.