Adventure on the Atari 2600 is more influential. Wizardry is probably more influential.

19 total to be exact when including TOTK unless you're including the CDi games, Zelda has been around since 85 which is 38 years as of now, in comparison other titles from that era in the likes of Mario, FF, DQ and so on go which are in the same legacy class hace significantly more releases go to the point that some titles became spin off series that have comparable amount of releases to Zelda for example the FF Adventure series became the Mana game. For reference mainline 2D mario games alone have thirteen mainline releases not far off Zelda's series total of mainline releases.

GameStop has some cool deals going.

Loftwing Amiibo for $5.

Skyward Sword is buy one-get one with other select titles.

re-tagging because my body is ready for Tears of the Kingdom.

Both very influential, no doubt, especially Wizardry for Japanese developers. All 3 trying to bring some aspects of tabletop RPGs into computer games (eventually it all goes back to D&D as most influential gaming IP in last 50 years).

But Ultima, as a franchise, did so many things that defined and influenced developers over its span and on so many levels (from overworld and openworld, to morality, to NPC's daily routines, to emergent gameplay, to MMORPG model with Ultima online) that is a shame that so few people know about it, and such a shame that there are no remakes, given how ahead of its time some of those titles were, and how much still some of those titles could teach modern developers.

TotK is the 20th Zelda game. You said mainline games so I did not count any spin offs, therefore I do not count any spin offs for other franchises either. Final Fantasy has 16 mainline games and Dragon Quest has 11. You can't only count mainline games for one franchise and all related releases for another.

But what if they turn out to be a separate monster?

Hm, didn't see anyone post this, thought it seems to be few days old now:

https://www.eurogamer.net/critical-roles-matt-mercer-is-zelda-tears-of-the-kingdoms-ganondorf

Matt Mercer is excellent DM, great at improvisation (though he calls for trivial skill checks way too often) and great at changing his voice, but apart from Critical Role I can't say I know how good of an actor he is - never heard anything he voiced, or at least not anything that I'm aware that it was his role.

I already like his Ganondorf voice. It's as charismatic as it is cruel. ^^

Yeah, it's pretty good. He has quite the range in his voices and inflections, it's a delight to watch every new NPC that he comes up with in Critical Role campaigns.