I used gdal2tiles to convert a bunch of GeoTIFFs to a tile layers , merged them and uploaded them to a webserver. The resultant URL looks like https://www.domain.tld/path/to/{z}/{x}/{z}.png , which I can use in LeafletJS.
My question is... is it possible to load this tile layer in ArcGIS? In my Google searches I came across https://wmts.maptiler.com/ which seems like it converts tile layers like what I described to a WMTS. I took the resultant URL and went to Insert -> Connections -> Server -> New WMTS Server and Servers -> WMTSGate on wmts.mptiler.com.wmts -> WMTSGate -> wwwdomaintld and was able to add that to the Contents panel but that then zoomed the map view out so much that the entire Earth showed up.
Any ideas?
You could use mapproxy (https://mapproxy.org) to serve the tiles. For output I've only tried WMTS once or twice, I normally use WMS services. I have been using it for serving aerial photos, hillshades, etc for about 6 years now. It works in Web App Builder and in Arc Pro.
Mapproxy is a proxy of course but what you do is stick your folder full of tiles somewhere and tell mapproxy that the folder is a cache. Then it happily handles serving them in whatever formats you specify, skipping the proxy part.
https://mapproxy.github.io/mapproxy/caches.html#file
You have to configure it with a text file so there is the usual learning curve. But it's not too bad. Also, it's free!