Hi there
You definitely do not need the -B addition if your version of scsynth is 3.8 That is what was current when SP 2.10 was released. I’m not sure why it is not linking to scsynth as it seems to be starting, according to the scsynth log. I suspect possible problems with the osc link to it, or the one linking the gui and the server. It is difficult to say without hands on your linux mint machine of which I have no experience.
You can see that even with Ubuntu 19.04 some have had difficulties. I have built SP using that script on a pristine virtual Ubuntu 19.04, but personally I am not a fan of script installs, because it is difficult to debug when things go wrong. I prefer to have a recipe of instructions and to carry them out one by one. That way you can see more easily when steps go wrong.
Most of the linux build recipes are very similar. They differ sometimes in package names for supporting packages. Often that is solved by looking at the library you want then searching the distro you are using to see which package installs it. You can get an idea from my Buster Raspberry Pi instructions, but I don’t think it would work on your model B which is unlikely to have enough memory. However building on Linux Mint shouldn’t be too much different from that.
EDIT
you might get some help from the author of this post