For the record I’ve the same problem on both 10.13.6 and 10.14 on two different macbooks. Overbridge 2.7.1 brought up an error and would not install. Downloaded it twice, tried 3x and 2x on respective machines.
And by the way, currently IMO it’s the legacy OS that’s the issue, not the hardware…yet! You can still update MacOS further than 10.14 on older macs, but it’s getting more difficult every year. Elektron stated that they’ll still support MacOS 11 (Big Sur) which is still compatible with some 2013 Macs onward, so needn’t be as expensive to upgrade as the jump to the M1 etc.
Also, if you stop wanting to buy new plugins etc and use what you have, it might not be such a big deal. Remember the other type - ‘perceived obsolescence’ includes users wanting the latest stuff when they already have plenty that does the job.