My sibling and I have been working on building a modpack. It works fine without Magnesium/Rubidium however when it is installed the game hard crashes any time I enter/create a world. We've also been experiencing chunk loading issues when the game does not instantly crash. Chunks from other worlds seem to overlap current chunks in the form of illusory errors. Ive been digging a little and I have updated BetterEnd Reforged to 2.5 but has not made any significant difference.
latest.log

You are using Magnesium and Rubidium at the same time, why? That is why it is crashing.

Lastly, if you end up posting an issue again, please post the log and crash report as separate files. Combining them together makes them difficult to read, and you did not communicate that is what you did either.

If you are making your own modpack, it is important to read the mod's documentation. Another thing you are going to have to do is know each mod's config files, worldgen, entities, and structures to craft an experience that is well balanced.

A good place to start if you want to learn how to do this well, is the FTB modpacks. Look at the changes and tweaks they have made to create the experience that they have. Unfortunately, creating a modpack isn't as easy adding a whole bunch of mods together. You can waste a lot of time creating a modpack when it would have been better just to use an existing one that already has the mods that you want.

Finding and learning from a modpack that uses good practices will put you much farther on your way to creating a good modpack, and ensure that the first one you create will be one you will want to continue playing and invest in. There are also highly popular modpacks, with millions of downloads that are not made well from the perspective of good practices, which you would not want to learn from even though they might be fun. FTB is a good place start.

My apologies I believe there has been a misunderstanding. We are not using Magnesium and Rubidium at the same time. The mod in question is just Rubidium though we did try them separately which yielded the same result. This is also not going to be an official modpack, just one for a few friends of ours. I appreciate the input and advice though C:

Here is the crash report as well I apologize for not including it:
crash-2022-09-28_17.06.42-client.txt

The crash report itself shows that you have both loaded from the log that you posted. That is why I said you had both loaded at the same time.

EDIT:
In addition, the crash report you just posted also shows you have rubidium and magnesium loaded together.

Lastly, whether the modpack is used by many or by few, by the masses or by your friends only, the difficulties and challenges of making a well ordered and decent modpack remain. The challenges are technical in nature and not rooted in who is the person playing it.