battery acid in remote control

I assume you purchased your Roku in August 2023.  However, it probably was sitting on a dealer's shelf for months, so you don't really know how old the battery was.  And my experience is that the batteries furnished in electronic devices are seriously inferior to the major-label batteries that you can get from a hardware/grocery/big box store, and they don't last nearly as long.

So suggestions:

First, using a cotton swab and a little water, remove the battery residue in the remote.  It's probably acidic, but it's not 'battery acid' in the same way that the electrolyte in a car battery is acid, but even so, you want to be a little careful with it.  If you have rubber/nitrile gloves, wear them, and be careful how you dispose of the swab when you are done.  Use a little paper towel to dry the interior of the remote after cleaning it, and dispose of the paper towel the same way you got rid of the swab. 

Then, install a fresh alkaline battery in the remote.  I won't mention any particular brands, but I will say that a battery from one of the major battery manufacturers will last much longer than a no-name or store-brand battery.  But the key word is fresh - make sure that the expiration date on the package is a couple of years out. 

Finally, when the remote starts acting sluggish, replace the battery.   The output of an alkaline battery declines somewhat gradually as the battery nears the end of its life, and that often causes a remote to be slow - you may have to press buttons a bit harder, or perhaps longer, before the TV responds, and that's a sign that the battery needs to be replaced.  You want to replace the battery before it gets so old that the electrolyte starts to leak out of the cell.

You may find other battery technologies available in your local store - old-fashioned 'carbon cell' batteries are less expensive than alkaline, and there are other technologies that are more expensive.  My experience is that carbon cells are a waste of money - alkaline batteries are simply far better - and while there are other, more expensive batteries available, they are better suited for specialized applications.  In general, the overall characteristics of alkaline batteries are ideal for ordinary, indoor household electronics such as remotes and smoke detectors.