My Mac is on OS 10.13.6 -High Sierra -which it appears won't support Mapbox GL, so how can I continue to use my (Paid-for) OS Maps?

As above - my Mac computer is on the OS High Sierra v. 10.13.6 . Which won't allow me to use the latest Firefox versions, and I am using the esr-update channel to run Firefox v 115. This in turn won't let me run the Mapbox GL you say is necessary to run OS Maps - which I have been paying-for and using without problems for several years. Since I am not prepared to buy a new Imac just to continue using OS Maps please explain how you advise me to get over this problem using my existing setup. If that is not possible then I will have to ask for a refund of my subscription and I'll use a different maps application.