I wanted to put this into my twitch modpack, but optifine cannot be included in the pack according to the twitch and optifine licencing rules. As soon as I take optifine out of the mods folder and attempt to run the game, it crashes before the game even opens the forge visual loading screen. After I press play, the launcher vanishes, then 5-6 seconds later, it reappears with an error.
crash-2019-08-07_11.27.43-client.txt

Nope, I do have forgelin installed. Just double and triple checked and even reinstalled it. It still crashes before launching with BetterPortals installed

You're missing Forgelin: https://www.curseforge.com/minecraft/mc-mods/betterportals/relations/dependencies?filter-related-dependencies=3
OF is a red herring (and tbh I cannot possibly imagine it having worked with OF but without Forgelin).

You must have gotten the incorrect crash report then because it unambiguously states that Forgelin is not installed.

Im not sure why the log said that at all, every time I got this issue I had forgelin installed. When I can, ill try and check to see if it is a certain mod messing up the loading process between BP and forgelin, or if there are simply too many mods.

I found the time to figure out which mod was messing up BetterPortals. It was VanillaFix. Not sure why they are incompatible.

No, that can't be it either. I've added explicit support for one of VanillaFix's features in 0.2.4 which involved quite a bit of running it alongside BP. I just tried BP 0.2.6 as well and it loads to Main Menu with no issues.

Im not sure, what the issue is specifically, but i know that in my pack, vanillafix will not run alongside betterportals. I didnt try all of the mods individually with vanillafix and betterportals together, but I disabled all of my mods and re-enabled them a few at a time. It only crashed again when i enabled vanillafix

Should i send a link to the pack on twitch/curseforge or give you a list of the mods im using?

I'm not up for installing random packs.
The correct crash report and/or log file is what I'm looking for (preferably the log). Chances are it'll already have enough information to tell which mod's causing it.

Also, in general, be more deliberate with your statements. Saying "It was VanillaFix." sounds like you tested just Forgelin + BP + VanillaFix and it broken, then you removed VanillaFix and it worked. It does not sound like you had tons of other mods in there as well, each of which could very well change things significantly on its own.
You might want to give this article a read.

I did some more testing, removing mods in clusters while keeping VanillaFix and BP installed. It crashed with BP+Forgelin+VF+P455w0rd's Library

I made a separate pack file with only those 4 mods installed. It seems that there is some kind of incompatibility triangle between BP, VanillaFix, and p455w0rdlib. I can have only 2 of those at the same time. Installing all 3 causes the game to crash before opening.

p455w0rdlib's coremod is broken, see p455w0rd/p455w0rds-Library#26 and p455w0rd/p455w0rds-Library#45.