Syria.
Iran has or is in the process of annexing a route through Iraq, Syria, and along the Golan into Lebanon (with its ally Hezbollah which runs Lebanon) to achieve access to the Med. Iran is stationing some battle-hardened troops 10km from Golan border; this is pre-positioning for an invasion and take over of the Golan - in conjunction with a coordinated attack by Hamas to the south.
The US State Dept (which historically hates Israel) has just announced the sale of 12 billion in sophisticated arms (helicopters, comm gear, night vision, etc) to Lebanon which is to say arms for Hezbollah and perhaps Iranian al-Qods troops.
As long as US troops are in Iraq and Syria, they present a check on Iran’s top military general, Senior General Soleimani ‘s plans. Withdrawing them means Iran has a green light to invade Israel (a standing goal of the mullahs that run Iran). So yes, we do have an interest in Syria: preventing a major regional war in the ME.
ISIS and Al Qaeda currently operate freely on the Golan border with tacit approval from Israel.
It seems more likely that is why battle hardened pro-Assad troops are gathering in the area.
“Withdrawing them means Iran has a green light to invade Israel”
You overestimate Iran’s capability, not their intent.