Are TR rewards from Max Raid Battles preset?

Yesterday, I did two Centiskorch (four star) Max Raid Battles while trying to find a TR for a good fire move. After doing both, I got the same TRs. I was wondering if the rewards, or at least the TRs, are set and if they are is it a permanent thing, daily, weekly, etc?

I definitely got overheat and I believe I got flare blitz as well. If the exact TRs are deemed to be necessary to answer the question, I will check them later tonight and add them to the question tomorrow.

Solution 1:

It seems that each "Den" has a set pool of Pokémon it can spawn, and each of these has their own reward table.

For example, Den #1 can spawn one of 8 Fighting-type Pokémon, most of which will reward TR21 or TR56, and some will reward TR39 or TR53, in addition to other items. Note that rewards will vary by den!

Serebii has been working on a database with all of this information in it, so you can see the odds of getting a certain Pokémon, and the odds of getting a certain reward from them. It looks like TRs are always 100%, and most Pokémon (especially evolutions) drop multiple TRs.

Source for Den #1. Use the selector at the top of the page to switch between the overview page and other Dens. You can find a specific Pokémon here, but if you're looking for a specific TR, it will take some more work.