At present, the Apple base stations still provide (up to WPA2-level) wireless security. They were designed as consumer-grade products, and like all other products of similar design, have limited overall functionality. Think of it as a trade-off between fully user configurable vs. "plug & play." Those of the former camp tend to be used by folks with mid-to-high-level networking knowledge; whereas the latter, are for most folks who just want it to work.
The bigger issue is not some much security with this base stations, but their longevity. As you noted, Apple got out of the networking hardware business in (early) 2018. Although they did provide a few updates since then, they haven't for quite a while ... and I don't think you will see any coming soon, or at all.
FWIW, I started "retiring" my Apple base stations soon after Apple announced that they will no longer be selling them. In my case I have an extensive background in both computing & networking ... so "upgrading" to a business-grade level was a "no-brainer" decision for me. I did this process, one base station at a time to ease into the new hardware, taking about a year to complete. Since then, with the features now available to me, I haven't looked back or would want to.
My only suggestion for you, at this point, will depend on your networking "comfort" level. Regardless, before venturing ahead, be sure to take the time to fully understand your networking requirements. Once you got those established, it will be much easier to wade through the many choices. One thing to keep in minding when "shopping" for new gear is don't rely solely on the manufacture's marketing hype. If you have questions, feel free to ask away. Folks here are always available to offer advice/assistance as you require.
