Being able to print out your invoices is a great way to keep a physical copy for reference. I can help go over printing options in your QuickBooks Online account.
QuickBooks Online provides many ways to send your invoices to clients such as emailing or printing a physical copy to help you save time. In order to print your invoice you'll first need to open the invoice you wish to print. From there select the print or preview option at the bottom of the screen followed by print. QuickBooks Online will automatically select the last option that you used when printing the last invoice for this customer. You can change this option by clicking where it says destination and then more options to find the printer you wish to use. If you can't find your printer in the list, that means your internet browser is having issues finding or connecting to the printer as QuickBooks Online uses your browser settings for printing. I suggest following the steps in this article if you're using safari and checking to see if it works when using another browser. If not you can get in touch with an IT professional to help get it set up on your browser again.
Hope this helps!