(I don't know how this will look in text mode. Hopefully it will be comprehensible in the archives.)
This is the summary of EXPLAIN (ANALYZE) on eight frequently-run complex queries from our application, extracted from the Postgresql log because either the BIND or SELECT takes longer than 3000 ms. I ran them each 13 times in succession, on otherwise-idle VMs with exact specifications. The 9.6 server runs RHEL6, and the 14 server runs RHEL8. The Planning costs are so high, I think, because the tables are partitioned using Inheritance. (This will NOT be changed, yet.) Naturally, Your Mileage *Will* Vary. Qry Num PG Version FIRST LAST MIN MAX MEDIAN Speed-up Pct *Planning* 01 9.6.24 17,922.488 18,160.742 16,695.140 18,580.261 17,741.328 14.10 13,176.262 13,483.961 12,934.866 13,689.540 13,483.961 24.00% 02 9.6.24 3,673.805 4,141.206 3,470.742 4,141.206 3,673.805 14.10 1,777.958 1,700.264 1,675.137 1,777.958 1,718.571 53.22% 03 9.6.24 239.675 268.971 225.361 348.565 271.909 14.10 218.283 220.856 215.588 225.895 221.485 18.54% 04 9.6.24 4,394.479 4,111.673 3,632.297 4,394.479 4,006.170 14.1 1,960.575 1,937.504 1,928.816 2,094.365 1,997.432 50.14% 05 9.6.24 3,674.314 3,876.537 3,192.784 4,105.541 3,789.318 14.10 1,790.975 1,753.901 1,677.151 1,846.911 1,760.372 53.54% 06 9.6.24 3,431.269 4,026.270 3,431.269 4,026.270 3,702.654 14.10 1,801.959 1,876.325 1,653.144 1,876.325 1,725.933 53.39% 07 9.6.24 4,273.917 4,268.979 3,888.995 4,553.267 4,157.208 14.10 1,914.381 2,006.053 1,914.381 2,042.719 1,980.043 52.37% 08 9.6.24 4,403.466 4,338.042 4,062.099 4,699.233 4,360.336 14.10 1,961.035 1,866.127 1,866.127 2,037.441 1,956.783 55.12% *Execution* 01 9.6.24 2,245.996 2,071.423 1,774.261 2,245.996 1,984.238 14.10 540.961 469.541 462.658 540.961 469.660 76.33% 02 9.6.24 36.875 37.047 33.718 40.299 37.513 14.10 31.910 29.618 28.387 31.910 30.284 19.27% 03 9.6.24 587.939 553.042 538.726 594.222 556.793 14.10 172.890 159.617 154.603 172.890 162.924 70.74% 04 9.6.24 1,068.230 1,081.044 1,022.087 1,100.884 1,068.230 14.10 157.058 161.618 157.058 167.006 160.243 85.00% 05 9.6.24 15.608 17.949 15.171 19.329 17.211 14.10 9.538 9.837 8.920 10.917 9.572 44.38% 06 9.6.24 54.796 53.216 53.216 67.378 57.401 14.10 60.135 50.899 47.108 60.135 48.267 15.91% 07 9.6.24 1,041.981 1,104.688 1,031.757 1,134.455 1,090.329 14.10 158.666 159.348 155.695 162.539 159.972 85.33% 08 9.6.24 1,142.164 1,160.801 1,103.716 1,249.852 1,191.081 14.10 159.354 155.111 155.111 162.797 158.157 86.72%