I personally try not to use Safari anymore and use Mozilla's Firefox instead. I too use Mojave on my 5,1 and feel no need to upgrade up with any dosdude type mod, since it runs fine with what programs I use. Seeing what type of extra items are added to the higher OS, like Monterey on my previous used 2014 mini, made me just want to stay put.
I've also left Safari on all systems now. I don't need a browser locked to the OS.
On the systems where I run Mojave and Catalina, I use Orion and Firefox. Unfortunately Firefox's support for Mojave is coming to an end while Orion doesn't support WebP pre-Big Sur, which is annoying. Brave was quick and supported WebP on those systems but they've now left both those behinds. I liked Mojave but 3rd-party support for it continues to dwindle (with more and more vendors gonig all the way to adopting Apple's N-2 support model).
Haven't decided what I'll switch to once Mojave, etc become unworkable for my needs. Neither Sequoia+ nor Windows 11, etc all that appealing.