Newegg is introducing a new trade-in system, which will allow you to get some cash for your old GPU. This trade-in policy places a value on your old GPU, and is usually preferred by those who don't want to step into the scary world of eBay and selling used merchandise online.
However, you're definitely going to be losing out on some value if you go in for Newegg's policy. The website itself explains the details, and shows us that we'll only be getting $561 for a used Nvidia RTX 3090 Ti, which is strange considering that Newegg itself values a refurbished model of that same GPU at $829.
Also, your GPU might not even be considered eligible for a trade-in, as Newegg has a list of criteria that needs to be fulfilled. If you're willing to sacrifice a lot of your old card's value, this might be worth taking a look, but it seems an odd first step. Also, it's worth noting that Newegg is a US-based company, so you might have to look elsewhere if you're wanting to trade-in in the EU.