One of the most frustrating things I find about jailbreaking is that you are stuck on the iOS you jailbreak. This is because you can only upgrade to the newest Apple iOS, which is rarely jailbreak-able yet, and that means you're either stuck on the old iOS or you'll lose your jailbreak for awhile.

Well there is a solution to this, involving something called "saving blobs" and something else called "futurestore". Please note that this requires some technical ability and you can fuck up your phone if you don't do it right, so watch out! Feel free to ask me any questions here. I am going to just link you to the good guides I found online which will refer you to this. Please read these and act on them in order.

Intro to Futurestore: (read this first)

Required preparation for iPhone XR/XS or newer (basically any iPhone released last few years):

Saving your blobs with TSS Saver:

Setting a generator:

Using Futurestore to upgrade iOS:

Note that you will not be doing the steps in the last link until you're ready to actually upgrade (i.e. the iOS you're upgrading to has a jailbreak), but you need to prepare all of the other stuff months beforehand (i.e. right now!)

As of the time of this writing, iOS 14.8 is the highest one with a jailbreak, even though iOS 15 has been out awhile. However, do all but the last link's steps now so you can prepare for when IOS 15 is jailbreakable.

Also at the time of this writing, the currently signed iOS are 15.3.1 and 15.4. This means that anyone doing this process right at this moment could only save blobs for future upgrades to 15.3.1 and 15.4. However, you will be given a link from the blobs saving page (TSS Saver) to keep checking back for future versions, in case you also want to save those. It is impossible to save blobs for unsigned versions, meaning today it is impossible to upgrade to anything earlier than 15.3.1, unless you saved blobs earlier.

The whole point of this exercise is to save your blobs for a currently-signed iOS so you can upgrade to it later once it's unsigned/old, but jailbroken!