This distribution of Linux is a Debian variant. It can turn a really old computer into an efficient workstation. What I like is that it has a built in ISO creator (an image file of your computer operating system and apps – similar to CarbonCopy Cloner for OSX) and Live USB application (boot into Linux off of an external USB drive). I’d go with XFCE as this is the one that is most supported.
https://mxlinux.org/
As long as the components of your old computer are working (powers up, monitor works, etc) you don’t need to buy a new computer for surfing the web, streaming videos are basic document and spreadsheet work. Convert it to a Linux operating system that only uses 14-16% of system RAM and give the old dog a new lease on life for the sake of productivity!