(x)tec Pro¹ using readily available cases and a small magnet, here is how.
Those cases are typically made of two parts: a synthetic inner shell glued to an outer leather book case.
Make sure you select a case that has a magnetic closure strap or it won't remain safely closed due to your device double thickness.
Artificial leather book case could work too but you may find that both inner shell and outer case are one and the same making them harder to customise. Moreover, while more compact, they often won't allow for F(x)tec Pro¹ thickness.
I've mostly been using SnakeHive Huawei P20 Pro leather case. However there are other brands with similar design that should work fine too. In fact I find SnakeHive leather quality rather inconsistent. The inner leather is often, but not always, given a smooth finish which I find unfortunate cause it's prone to register screen touches. The outer leather has more of a suede finish. However apparently you can easily turn smooth leather into suede. Also the inner shell on the SnakeHive is made of ugly transparent and poor quality TPU. It's notably too soft. Therefore it makes sense to replace the inner shell with one of higher quality.
EasyAcc Black TPU. It also features holes to attach a wrist strap or lanyard. When selecting your inner case make sure it's made of soft material as hard shells are unlikely to fit your F(x)tec Pro¹ on top of not easily allowing for custom cut-outs.
On that one the inner side with credit cards slot was replaced with a thinner layer of leather.
Here we are showing examples of small magnets with 15mm and 10mm diameter.
Both should work though the larger one could be easier to fit as it should not require such precise placement.
Location of 15mm magnet on SnakeHive case:
Location of 10mm magnet on SnakeHive case:
Fx Service. That will notably allow you to lock your phone as you close your case and wake it up as you open it.