I want to sell some of my CS:GO skins for real money; and as far as I know, using an online marketplace similar to the one on Steam is the best option. However, I noticed that after depositing my skins to the platform, I will have to wait for 14 days of the Steam trade hold and only then start selling, which also may take some weeks. So, my problem is that I don't want to wait for 2 weeks before they will be available and want to sell them instantly. Is there a way I can do so?

yes, just use sites that can sell skins directly, without bots; for example, dmarket - https://dmarket.com/ingame-items/item-list/csgo-skins

^ dmarket is top notch. user friendly too

As far as i know you cant sell it on steam market maybe on some sites

You need to have the Steam account without the limitations, meaning you need to have atleast 5 euros in the account to trade and use custom sites for trading CS:GO skins.