Apart from searching specific cards, you cannot easily find new cards that have been released. Say like Set:SPG is a bit of a secret when special guest cards are released to MTGA.

So when you add cards via:
https://magic.wizards.com/en/news/mtg-arena/announcing-the-arena-powered-cube

and say "The initial list of cards on the bonus sheet are:" and "More cards will be revealed throughout the week. Check out Luis Scott-Vargas's and Paul Cheon's YouTube channels on October 22 for more updates!" This implies that there will be MORE cards than just the listed cards.

I cannot name one specific set or look up an anthology to see this. Would be easy to make a new list “Set:Other Bonus Sheets”.

Sometimes only looking at new cards is helpful. Like on Scryfall, I can open up the set drop down and see TMT, ECL, TLA, SPM as direct to Magic (the bonus sheets and sets that take more research can still be found: when you type ‘Avatar’, then I see both TLA and TLE sets).

When MTGA was first released the search tools was a solid B grade. However plenty of new symbols and partial sets exist; that you cannot easily find what you want. Like phyrexian mana can be searched but you need a 3rd party to tell you how to use MTGA fully or just use Scryfall to search for said phyrexian mana.

It is time to update MTGA search tool.