Early in the 5E era there was far less WotC products to buy. That makes this an odd question.
Here are the core books and campaign guides available for sale by year:
2014: 3 Core (MM, DMG, PHB)
2015: 1+ SCAG (bonus: Free Elemental Evil Player's Companion)
2016: 1 VGtM
2017: 1 XGtE
2018: 2 GGtR, MToF
2019: 2 AI, EBftLW
2020: 3 TCoE, EGtW, MOoT
2021: 3 FToD, VRGtR, SaCoC
2022: 3 MPMotM, Spelljammer, Dragonlance
We've had 2 Campaign/Adventure books per year fairly consistently.
In terms of physcial purchases, I bought everything through 2018, then about 1 book per year for the last few years.
However, I have purchased all of the above (through the 2021 materials) on D&D Beyond. A lot of these books are fun to have on D&D Beyond, but I will not miss not having them down the road when Beyond closes shop (which I assume it will - although it would be great if they gave the books to us on pdf at that point as encouragement to go with them for the next edition). I may buy some of them in used book situations in the future, but I hardly crack my physical books now, and I imagine I will move on from 5E when 6E comes unless it takes a 4E style right turn.
For 3rd party, I have only 3 in the 5E era, and 2 of those are Critical Role which is a psuedo WotC as you get. The last was a purchase I made to use up some store credit before I moved - Courts of the Shadow Fey.
However, as I see them 'playtesting' changes in the mechanics in recent products, much like they did at the end of 3.5E and 4E, I am hesitating to buy materials these days. Buying a product in 2017 when I thought 5E had at least 5 more years to go was a good deal... but as I think the edition has less than 5 years less, I am less likely to buy it now as it has less use - and it is competing with more stuff that I already own.