Hi Adam,
The geometry for a Flaanimal is not designed around a 100mm suspension fork, so for sure you would be pushing up the front of the bike and slackening the head tube a fair bit. A few people have done this and report having quite a lot of fun on it, but it’s defintiely not the core use of the frame as-designed. I would actually recommend sizing the frame down one size if doing a suspension fork such as this, as this would offset the increased stack height of the suspension fork, but would still slacken the head tube, which would actually bring it more in line with MTB geo.
This would be best considered with the help of something like Bike Cad to really do the work understanding how to select the right stem height and length as well, so that you can find that optimal riding position in the context of the new geometry.
I hope that helps a bit!
Stephen