Me and my friend primarily use this mod for keeping the server ram lower but it's annoying having to re-explore the chunks to be able to see them from far away again, is there a chance that we could be able to save chunks on a server after relogging? I noticed there's a mod called bobby that does this, but it crashes me so my only option is this.

I would also be happy to have this function too.

there is pros and cons to that functionality, it adds a decent bunch of complexity overhead and does also use more resources on your machine(cpu core for loading/saving things to disk, disk space). And the added complexity also introduces more bugs, as you can see with bobby

Plus here. You do not need very intensive disk IO. Save periodically only in a separate low-priority thread. Reload slowly, not all at once etc. Distant Horizons mod does it, but, unfortunately, it is not supporting well Embeddium/Oculus and the decreasing of the render quality of far land drawing is too bad.

Sorry to bring this up, but, yes, that would be a good addition, it can be made as a toggle, so that a player would chose what mode he wants to use (or just a different fork of the project). Not to mention, that 1.12.2 misses that kind of mod (i mean, it is old, but a lot of modpacks are still made to this version. Also, recently, the 1.12.2 fork of this mod was updated, so i still hold hope for further development). There is a FarPlaneTwo, but it is very raw and works by an absolutely different principle.
P.s. i can understand if the feature won't ever be implemented, but we'd really like to see it
Upd: Just noticed it's a duplicate of #26, but still, i should give it a try, maybe you changed your mind

I was looking for this exact function, it is one of the last ones that is not available.