I love my reMarkable, but I passed on the way overpriced case as well. However, I bought the one linked below, and I am sure others are available. It has a seated magnetic strip in the folio’s binding and then depressions for the feet on the back of the remarkable so that it sits flush. The reMarkable sits extremely snuggly in this book folio and I haven’t had any issues.
Ayotu Case for Remarkable 2 Paper... https://www.amazon.com/dp/B094NBGG78?ref=ppx_pop_mob_ap_share
Edit: didn’t realize OP purchased a third-party case. Changed my wording to match.
It depends on where the magnets are located in the case. Remove the RM2 from the case and then use a paperclip or something like it to determine where they are located. If there are magnets directly behind the writing areas, the it could be a problem. What I discovered is that I had other sources of magnetic interference such as the lower portion of my laptop where I would often rest my RM2 when writing which was causing mine to have issues.
I have this case and the magnets are only near the edges which have no impact on the writing area. Amazon.com: Ayotu Case for Remarkable 2 Paper Tablet 10.3" 2020 Released, Book Folio Design with Bulit-in Magnet, Premuin Fabric Smart Cover, Only for Remarkable 2 Paper Tablet, Not for Remarkable 1 : Electronics
I konw you are wary of magnets but this one has been wonderful for me with zero isues
This case is practically identical to the more expensive ReMarkable 2 folio, and just as good in my opinion.
https://www.amazon.com/gp/aw/d/B094NBGG78/
As for the ReMarkable 2 pen (with the eraser end), I like it the best of all pen options, but the less textured surface of RM2 makes other pen options appealing (I have quite a few alternatives).
Samsung Galaxy Tab 6 S-Pen (writing feels good, no eraser) Staedtler Norris (regular) pencil (pretty much same as above, but too smooth feeling for me) Staedtler Norris Digital Jumbo (probably my favorite alternative, feels good and eraser end works out of the box with no hacks required) Lamy EMR (feels a little scratchy and, for whatever reason, seems to write lighter than other options) Galaxy Tab S3 S-Pen (feels nice, about the same as Tab S6 S-Pen but the form factor is better... Not as skinny and has a clip) Galaxy Note 10 Plus S-Pen (too small, but works in a pinch. For some reason this S-pen nib feels the best writing on RM2. Not sure why that is, as the other S-Pen tips should be the same?)
I would recommend the folio above and probably the Staedtler Jumbo if you want to save money. You will just be sacrificing a bit of the OEM Marker Plus feel, but it's negligible (in my opinion).
I got this book folio, which I am very happy with. https://www.amazon.com/gp/product/B094NBGG78/ref=ppx\_yo\_dt\_b\_asin\_title\_o01\_s00?ie=UTF8&psc=1
I have the polymer book folio and it works well. This replica is being sold on Amazon for a fraction of the price, but I have not tried it.
https://www.amazon.com/gp/aw/d/B094NBGG78/ref=ya_aw_od_pi?ie=UTF8&psc=1
I have this one and its really slim and uses magnets to connect to the side. I just toss it in the case if I'm putting it in a bookbag or storing it.