What is the maximum stay duration in Thailand using visa exempt entries and tourist visa extensions?

Keep in mind the visa exempt entry is now 45 days not 30 so you can get a total of 75 days in country with a visa exempt entry and the one 30 day extension you can get from it,

AND

the limit of two visa exempt entries is in a calendar year (Jan 1 to Dec 31) not a 12 month period, so it resets on the new year..

If what you're asking is "can you live here on back-2-back visa exempt/tourist visa & extensions" the answer to that is NO. This isn't like the thailand pre-covid where people could live here for (sometimes for years) on v/e, tourist visa and extensions.

As Lloyd pointed out there is no official limit to visa exempt entries by air, but after a few especially if they're back-2-back they're going to pull you out of line and ask WTF you're doing living here on free stamps 😮

Same goes for tourist visas. It's just NOT a viable way to live here any longer, you might get a few visa exempt entries; take the two allowed by land in a year and then a couple by air entry) or a few tourist visas; but you'll have to use different consulates each time BUT you will get called out on it sooner or later.

That would all depend on how you plan to border bounce, in theory if you do it by air, there is no limit, however if you do it by land then it is only twice in a calendar year.