It's just not true at all that most older phones cannot be updated regularly to the latest versions of Android. Manufacturers choose not to support those devices as they want to sell a new phone to you.
But 3rd party custom ROMs do exist for older phones and often give you the choice of whether to install the Google apps or not. Apart from getting the latest features (hardware permitting) and patches, these ROMs are often include extra features that you don't see in standard Android, and you also usually have a more privacy orientated OS.
The downside is you usually have to do a manual flashing the first time, but after that most ROMs will auto update just like standard Android does.
The site below lists the phones that can install these custom ROMs.
Want a taste of Google's latest Android 11 update but don't want to wait for your manufacturer? Check out our list of custom ROMs!