1) Go the page with the PDF manual for your model on Motorola's website, and there's a Download link in the upper menu bar to save the PDF to your phone, or wherever. (...or use the download function of whatever browser app you're using).
https://help.motorola.com/hc/1764/90/pdf/help-moto-e6-play-90-global-en-us.pdf
2) Peruse through Settings menu of your phone to just disable the startup sound. In my Moto phone the option is in Settings >> Sound >> Power up sound. It might be in a different menu or sub-menu in your phone, or showing in a slightly different name (i.e. Boot up, or Start sound, or whatever). There's a lot of things you can do to customize and/or optimize your phone's settings and user interface if you just take the time to familiarize yourself with the Settings menu. Keep in mind there are a lot of options and things so keep track of anything you do alter just in case you inadvertently disable something vital or important so you can enable it again. And there are a lot of contextual items so there are often a lot of different sub-menus that might be buried in an icon (gear icon, three-dot icon, three bars icon) that might be in the upper or bottom menu bar)
3) and 4) Once you format a microSD card to be 'Internal' that alters the card in multiple ways. By default it will be formatted with either FAT32 or exFAT, an outdated, unsupported but still proprietary, and limited file system from Microsoft. Leave the card as Portable and it doesn't alter the card. Once you reformat the card as Internal though, that changes the file system to be ext4 (to work in unison with also ext4 internal storage media), and the card gets encrypted (the encryption key ties that specific card to that specific device, and the encryption key gets stored within the phone's internal storage in a protected system-level directory).
Since it's not known if you did or didn't use either Internal or Portable on your other phone, than there's an issue with the card either encrypted via formatting it to Internal or the card was just encrypted using the Settings >> Storage menu on your other phone. Either way the card's file system has been directly tied to that phone, that's a
security aspect. It's not a problem or a bug, encrypting storage media is a security feature. If you encrypted the card and where actually able to just freely use it with other devices, THAT would be a serious problem. If you want use that card in other devices again, you have to reformat it again. That returns it be to FAT file system and remove the encryption (and yes, all data on that card gets wiped in the process).
