Samsung have great security, and the GrapheneOS team said multiples times that it’s one of the few manufacters that meet their security requirement. Unfortunately Samsung does not allow you to easily unlock the bootloader anymore and you CAN’T relock it after installing an alternative OS. This is the main reason why GOS is not available on Samsung device.
You can try LineageOS or /e/OS, both should have a build for your device but keep in mind that your security will be somewhat degraded. Your phone isn’t supported anymore anyways so it might be beneficial depending on your threat model. As LineageOS and /e/OS are way less bloated than Samsung stockROM you could benefit from better performance in several ways. I have revived a few device with LineageOS and DivestOS (RIP). If you buy a new one I would consider a Pixel 8A or 9 depending on how much you want to spend, they will benefit you from years of security updates.
From my experience I never had any issue with calls or mobile data on GrapheneOS nor any alternative ROM installed.
Honestly everyone is different and so has different needs. I have been running on my main devices CalyxOS for a couple years then switched to GrapheneOS after buying a Pixel 6A and the only downside I have with this device is battery life which is not amazing. They have improved that significally with their last gen devices (Pixel 9, 9 Pro and 9 Pro XL) and it doesn’t seem to be an issue anymore while still not be really better than the competition. I have also run other OS on secondary devices and honestly didn’t cared about their security as much as my main device.
Your device hasn’t recieved security updates for more than 3 years now, so if you don’t feel afraid, or in danger of being hacked with a strong negative impact on your life installing LineageOS or /e/OS on your device will not be stupid as you will benefits from newer security patches and feature updates. You will lose some protection such as the unlocked bootloader but for some people it’s okay.
You don’t need maximum security but you will probably benefits from it. If your phone is still running well and that you don’t wan’t to change it yet it is okay. If you feel like it’s important for you to upgrade your security by upgrading your phone consider buying a relatively new model that will have at least 4-5 years of security updates, since it looks like you’re keeping phone longer than most people does. You can lose freedom and buy an iPhone. Or buy Google hardware and ditch their software. If you want to buy a Samsung, a OnePlus or whatever and flash LineageOS on it I think you’re better keeping your phone with LineageOS for a bit longer. You can also debloat a OnePlus, etc but it won’t be as degoogled as you may want it to be. Still more secure than flashing LineageOS on a currently supported device. Remember that Privacy ≠ Security.
That’s my opinion I am not a security expert