why does a font previously downloaded doesn“t appear in my fonts

I do not know what you mean with "my fonts", so please be more specific.

If you want a font to be available in your software, make sure you have installed it. You can either manually install a font or use a font manager.

thank you for answering, I already installed it and ican“t find it on my software Itry to use it but it doesn“t appear on my avaiable fonts

Better use a font manager. Not sure if you have a Mac or Windows, but a good Windows font manager is MainType and it comes with a free edition.
https://www.high-logic.com/font-manager/maintype

thanks a lot I use a Mac which app can I use for managing my fonts

Use FontBook

https://support.apple.com/es-mx/guide/font-book/welcome/mac

https://support.apple.com/es-mx/guide/font-book/fntbk1000/10.0/mac/10.15