Indirectly. Newer firmware (B12+) includes better antenna switching algorithms. However, firmware cannot create signal where none exists. For signal issues, focus on external antenna modifications (the MC888 has two SMA ports hidden under rubber plugs).
Here is where the search term gets interesting. The stock firmware locks the ZTE MC888 to your carrier’s band preferences. Advanced users like to flash to turn the MC888 into a universal 5G router. zte mc888 firmware work
ftp://ftp.zte.com/pub/Consumer/5G CPE/MC888/ Indirectly
Ironically, many "firmware bugs" are actually heat issues. The MC888 runs hot. If the firmware detects 85°C+, it will throttle to 100Mbps. it will throttle to 100Mbps.