Hello,
Some Acer models have options for touchpad in BIOS and needs to be set from Advanced to Basic in order to properly work on Linux.
You can also check if somehow the Fn key is not mapped to the Window/Meta key, so once you press it in combination with something else the touchpad is disabled.
You also had the suggestion on this post Synaptics driver for acer 515-56 - #12 by chicho1704 to switch from synaptics driver to libinput and also the Touchpad Synaptics - ArchWiki points to the fact that:
So, in the end what driver are you using and what have you tried so far based on those wiki troubleshoot pages?