TL;DR - it's possible to get more than one GV number; you can only use one at a time; here's how and why it can be useful.
FWIW, linking a GV number to a "real" mobile number is only really needed when you to take ownership of the GV number, solely for verification purposes (it's one SMS message with a 6-digit code, just like any other MFA).
Once you have the number in your GV account, you can unlink the "real" mobile number from the GV number and they are completely separate again. So, if you already have a GV number and really want another one, find a friend that will let you use their phone for the SMS verification code, then unlink their number right afterwards. Viola, you have another GV number. The caveat is that the friend can't then use their number to get their own GV number, so make sure they don't care.
If you have more than one GV number (so, multiple Gmail accounts), you need to link the one you want to use to your actual mobile number under Google Voice > Settings. You can link/unlink as many times as you want, which means you can change which GV number is tied to your phone any time you want. You can NOT link more than one GV number to your mobile number simultaneously.
This came in handy for me because I wanted to add another line to my cell phone plan, but if I didn't bring a number with me the carrier would force me into a higher plan ($35/month) for that additional line. If I brought a number with me it was only $15/month. That's $2,400/year! Ridiculous! Google only charges three dollars to unlock a GV number, which allows you to port it to the carrier of your choice. When you add the line the carrier will port it over for you. So, there are some instances where this can be useful.
This is all true as of November, 2023. Who knows if Google will decide to change things up someday. Hope this helps.