Offline wallet.dat storage for large volumes

I would like to store my Bitcoin wallet offline, but I need some guidance. Since this will be my long-term savings storage (moderate amount, rarely accessed), to make PSBT I have one PC (online) with just Ubuntu and Bitcoin Core installed, and offline only with Wi-Fi/Bluetooth/networking removed. We will be using one PC. It only uses Ubuntu and Bitcoin Core to generate wallet.dat and sign PSBT if necessary. Now I want to store wallet.dat in various places so I don’t lose access to it. I can’t find a detailed guide for this process.

For example, is simply encrypting the wallet.dat file sufficient? I want to avoid using third-party software (e.g. truecrypt) as much as possible, because the project could be dead in 10-20 years and it’s difficult to get reliable software packages, etc. in the beginning.

Also, what media is best for long-term storage? CD, USB memory, microSD? Will any of them rot? Remember, we’ll need this accessible functionality for decades to come. Are you planning on burning the wallet.dat file to a CD, considering that this kind of media rarely interacts with my PC, unlike USB sticks where backdoors can be used? There are also objections to uploading this to the cloud (if encrypted).

Sorry if this has been answered. But what I found is a bit outdated and doesn’t seem risk-averse enough for the value of Bitcoin these days.

Any help would be greatly appreciated.