The file "index.html.tmpl" of weewx v4.8.0 contain slightly different lines than the one suggested but we went ahead and did these changes:
replaced this
#for obs in $getobs($plot_name)
#if getattr($recent, $obs).has_data
#set $show_plot = 1
#end if
#end for
with this
#for obs in $getobs($plot_name)
#if getattr($recent, $obs).has_data or $plot_group == "aqi"
#set $show_plot = 1
#end if
#end for
and it did work and the plot was shown on the webpage.
but how we can expand this temporary fix to include "aqi1" which belongs to another sensor and another data base "aqi1.sdb"
we tried
#if getattr($recent, $obs).has_data or $plot_group == "aqi, aqi1"
#if getattr($recent, $obs).has_data or $plot_group == "aqi; aqi1"
#if getattr($recent, $obs).has_data or $plot_group == "aqi", "aqi1"
none worked and weewx did not complain of these changes or gave any errors but refused to show the plot of both "dayaqi.png" and "dayaqi1.png"