If it were me, I'd be looking at exactly what my needs are in terms of software, and workflows. Whatever computer is in use is merely a tool to achieve the required results, and if the existing tools work, then they don't need changing.
The problem would come with hardware that is getting older. Not because it is inherently less reliable, because generally that isn't particularly true, but because it is slow, relatively speaking.
The degree to which that matters depends on the work being done, and broadly, as long as the software doesn't change, and the work remains based on the same data volume, there isn't any great need to upgrade - either hardware or software.
Unless software 'times out', the fact macOS may not support later versions than the one in use matters very little either. This is why for some people it is still possible to use G5/G4/G3/68k Macs for productive work, even now.
All of which means that if it were me, I would be happy to stick with what I already have if it still works for me the way I want it to, and still gives the results I need. But, if I were to find it lagging, particularly in being able to deliver results in a timely fashion through performance degradation or software restrictions, I would look to upgrade, based on the realization that the time I was losing to poor performance costs money, and that a new system would potentially pay for itself reasonably quickly as a result.