From your second alsamixer screenshot, the HD-Audio Generic one.
Can you adjust volume (using up arrow) of the "Master" and "Speaker" channels?
Also unmute "Headphone" channel by selecting and hit "M" key to unmute. Then try increase volume of that channel.
I am also wondering, if a fairly new (AMD chipset) laptop, as support of AMD is provided by linux kernels, maybe installing a later linux kernel may be an idea.
Thanks for responding!
So, with the arrows I can only increase master but not speaker (if I press on it and try to increase with the arrows, nothing happens), which is apparently the only thing I cannot control in that "screenshot".
Concerning the headphone channel, I can modify that one too (both if I mute or unmute it) but without any conseguences. Also, I've noticed that the sound "becomes better at 100%" only if also the bass channel is set to 100% (apparently, if it is enabled and set to 100%, it adds some "high frequency" to the sound), otherwise sound quality doesn't change at all between 1 and 100%.
Concerning the linux kernel, how do I do that? Don't know if this matters, but this is a fresh zorin installation from a few days ago
ZorinOS is based on a stable LTS version of Ubuntu. It is not at the cutting edge of linux development and intentionally so. As AMD kit is supported by linux kernels (a good thing) as linux kernels progress newer AMD kit is supported. I am wondering if your machine is so new that it may need a newer kernel.
Maybe others here can chip in and help to decide if that is a worthy direction to follow in the case of your specific AMD spec.
The process of installing a later kernel has been covered on the forum many times. e.g. [HOW TO] Easily install a later Kernel (Needs Net Connection)
Should be worth a Try with a newer Kernel.
Ok then, thanks so much again for the answers! I'm going to update the kernel and keep you guys update here
OMG IT WORKS NOW!!!!! Thank you so much!! I've been trying to fix it since about a week but now it perfectly work! With kernel 6.19.4 
Yes it actually was the solution! Thanks so much to you too!
Apparently updating the kernel was the solution! But thanks so much for your help and patient too! 
I'm glad all is OK for you
@wat
glad you got it sorted
best of luck Steve ..