I don't believe you have much success in selecting a suspension fork. Looking at the bike, a suspension fork with exactly same geometry as yours would have approximately zero suspension. There is simply no room for a suspension fork with unchanged geometry. If you change to a suspension fork, it will change the geometry of your bike which will affect the steering characteristics. For example, the seat tube angle is changed (so you may run out of fore/aft adjustment in your seat post), the head tube angle is changed (so the fork trail affecting the steering characteristics will probably not be what the fork manufacturer intended), the bottom bracket height will change (so you will find it harder to mount and dismount due to increased bottom bracket height).

Every frame will have different requirements for a fork. If you see a fork, you need to carefully look at its dimensions and analyze what the fork trail will be and how the bottom bracket height and seat tube angle will change. Only with such an analysis can you determine if the new geometry of the frame/fork combination is acceptable.

A bike frame designed for suspension would have reduced head tube height from the lower end, making room for suspension below the head tube. For such a frame, the intended fork length is longer.

Juhist's answer correctly describes the trouble you're signing up for in your endeavour. Remixing your bicycle's whole geometry is not undertaken lightly.

One thing you may not have considered is a suspension stem. Redshift makes one that is on sale just inside your price point. There are others forthcoming, and a big list of styles and discourse at CyclingAbout, including some downsides:

Why should you avoid suspension stems?

The biggest issue is that any downward force to the handlebars will result in energy loss. This is not great for people who like standing up on the pedals, but shouldn’t be much of a problem for people who spend most of their day in the saddle. An issue that the 90s suspension stems suffered was movement under heavy braking. I presume that this effect is lessened on the latest generation of products given how much less suspension travel there is.

I don't think energy loss is much of a concern for an ebiker. You can just throttle up rather than stand on the pedals.

Please note that I have not used a suspension stem myself. If I were in your place, I'd put 5-20€ toward a pair of cycling gloves before I spent 100€ rearranging the front of my bike.