cleder / fastkml

>>> k = kml.KML()
>>> with open("/content/001AAN005121.kml", 'rt', encoding="utf-8") as myfile:
>>>   doc = myfile.read()
>>> k.from_string(doc.encode('utf-8'))
>>> features = list(k.features())
>>> len(features)
0
>>> k.to_string(prettyprint=True)
<kml xmlns="http://www.opengis.net/kml/2.2"/>\n

Full KML:

<?xml version="1.0" encoding="UTF-8"?>
<kml xmlns="http://www.opengis.net/kml/2.2" xmlns:gx="http://www.google.com/kml/ext/2.2" xmlns:kml="http://www.opengis.net/kml/2.2" xmlns:atom="http://www.w3.org/2005/Atom">
<PhotoOverlay>
		<name>001AAN005121</name>
		<Camera>
			<longitude>-43.14191969918544</longitude>
			<latitude>-22.94609248078273</latitude>
			<altitude>13.51429618609447</altitude>
			<heading>-100.7587511189315</heading>
			<tilt>95.13099352600476</tilt>
			<roll>0.6257414686006844</roll>
			<altitudeMode>absolute</altitudeMode>
		</Camera>
		<Style>
			<IconStyle>
				<Icon>
					<href>:/camera_mode.png</href>
				</Icon>
			</IconStyle>
			<ListStyle>
				<listItemType>check</listItemType>
				<ItemIcon>
					<state>open closed error fetching0 fetching1 fetching2</state>
					<href>http://maps.google.com/mapfiles/kml/shapes/camera-lv.png</href>
				</ItemIcon>
				<bgColor>00ffffff</bgColor>
				<maxSnippetLines>2</maxSnippetLines>
			</ListStyle>
		</Style>
		<Icon>
			<href>https://imaginerio-images.s3.us-east-1.amazonaws.com/iiif/001AAN005121/full/max/0/default.jpg</href>
		</Icon>
		<rotation>-4.02</rotation>
		<ViewVolume>
			<leftFov>-26.2</leftFov>
			<rightFov>26.2</rightFov>
			<bottomFov>-16.335</bottomFov>
			<topFov>16.335</topFov>
			<near>4.54261</near>
		</ViewVolume>
		<Point>
			<altitudeMode>absolute</altitudeMode>
			<coordinates>-43.14191969918544,-22.94609248078273,13.51429618609447</coordinates>
		</Point>
	</PhotoOverlay>
</kml>

Is this caused by lack of PhotoOverlay support?

Yes there is no PhotoOverlay support at this time. It should be relatively easy to implement:

fastkml/fastkml/kml.py

Line 616 in 027a504

class _Overlay(_Feature):

currently working on it in here

from_string() does not recognize PhotoOverlay features