This was previously possible with the Google Tag Manager code and Universal Analytics property, but since Universal Analytics is being sunsetted and Google Analytics 4 is the new default, it's not clear whether or how this is possible, and unlike with Universal Analytics, there don't seem to be any guides detailing the process.
Is it still possible to track mailto clicks as conversions with Google Analytics/Google Ads?
Yes, it's still possible.
The inherent ability to track clicks does not lie within GA UA/GA4. Tracking is done separately, often in GTM. What happens on that tracking - whether it's a UA or GA4 event has no influence on the tracking.
Exactly the same logic applies to G ads conversions.