4vorvieri has described the facts very well... the handles (whether wooden or plastic) are secured with Loctite (or a similar extreme glue) on Lelit. The method he describes works... except that I sprayed WD40 into the joint beforehand and let it soak in. You can't get replacement handles from Lelit as far as I know, and not all you can buy online (Amaz***, Ali*** etc.. fit :-((.
Same goes for the spout by the way....
Have fun & Happy Holidays

The handle is secured with a special glue. It takes an enormous amount of force to loosen the plastic handle. I clamped the plastic handle in the vice (this will almost certainly break it). Then I heated the threaded area with an industrial hot air blower. Turn the sieve support, for this I adapted a longer piece of squared timber for the inner diameter. The portafilter can be turned by means of leverage. Have fun.

I have this portafilter, it's great, no plastic, it's wood and stainless steel.

The plastic handles are screwed on from behind. However, these are not replacement handles, but a complete portafilter.