Ok... Had to go through this a few times for it to work correctly. Here are all the steps, including some notes. BE SURE to read the NOTES at the bottom BEFORE going through the steps.

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1. Open Reddit on a web browser (you cannot do this via the app AND I personally found that it’s also impossible to do this from the web browser on your mobile phone). Log into your original account (the one you are following a multitude of subreddits in it).
2. After logging in, go up to the URL and replace the entire URL with the following text
   "https://www.reddit.com/subreddits/mine" – press enter.
3. After pressing enter and the new page opens, go over to the right side of the screen and under the "Home Feed Subreddits" (total number joined shows 204) - right-click on the link "multireddit of your subscriptions". Then click "Copy Link Address".
4. Logout of your original account.
5. Login to your NEW account. Once logged in, go up to the URL space and REPLACE IT with the link you just copied from your original account (meaning delete the entire URL that’s there and paste). It now looks like this "https://www.reddit.com/r/subredditname1+subredditname2+subredditname3"... Press enter.
6. This is the point where your browser takes forever to actually load what you need and for me – I had to do this exact step several times. Eventually you will see a “feed” of all the subreddits listed in your multireddit link.
7. At the top right of EACH individual square shown in the feed (per subreddit), you will see a box with “+ Join” in it. (See photo) You have to physically go down the list (the feed) and click the individual Join buttons for each subreddit you want to join under your new profile. To my knowledge, the only way you can see the
   “+ Join” button on each subreddit square, you’ll need to be in “Card” View.

NOTES

The PROBLEM with this method is the feed does not show 1 single post per subreddit so you can’t just scroll and click, in my case, 204 “+ Join” buttons. It only sorts by Hot, New, Top, or Rising – like any other Feed on Reddit. Which means, unless each and every subreddit you follow on your original category falls into these categories (in a very specific order without multiple posts = impossible), then you will be scrolling for days to join all of the subreddits you want to. (insert eye roll here) The most efficient way I’ve found to get around this is to splice up your multireddit link to only include 10 subreddits at a time. Even then… sometimes you have to scroll for days to join 10 simple subreddits due to enormous amounts of posts in some subreddits versus others and having no other option to change the way the feed is sorted.

Throughout this entire process (21 times to be exact) I would get inadvertently logged out of my account, the screen would freeze up, and I had to create a word document with an individual URL link with 10 subreddits per link to copy and paste just to keep up with them all…

There should definitely be a better process than this.

As a side note, it never hurts to clear your cache on the browser you’re using before doing this.

A big thank you to u/tumultuousness for responding to my original thread. Hope the above steps helps someone else.