How to stop Excel Online from being so slow?

Since an update a few years back, I want to say two or three (it was some UI changes mostly) my Excel Online has just been unbearably slow.

Just a few minutes ago I added a new sheet to an existing file. For some background it was previously a single sheet 13x47 table with 2 columns of simple calculations (one adding up a couple columns, and another doing some division), 282 cells being used. The new sheet took 2 minutes to process and actually be created. It is currently a 6x21 table, but by the time I created the 3rd of 6 columns it froze and had an error then reloaded itself putting me back to only 2 columns made. It did this again then 3 times more before I finished the table, each time taking several minutes.

There is not a lot of data in the file, there's simple calculations without function calls, and I have no issues with my internet connection. I could make a new file and still have the same issues. I often have to reload a file 10+ times before I can complete some simple data entry.

I do know there's a banner that pops up from time-to-time about my internet settings but clicking the hyperlink that comes with it just crashes the file again. I also know that Firefox (the browser I use) will occasionally try to get me to close the page because it's lagging out so bad. Lastly, the files work fine on my phone browser.

Anyone know what could be causing this? Because at this point it's honestly faster to use pen and paper if not for the fact I already have all the old data online.