Shimano and KMC 11 speed chains sold for road systems typically will come with 116 links of chain (in this case the 116 refers to each pair of inner plates as 1 link and each outer pair as 1 link, when technically, those are half links as one pair of outer plates and the adjacent pair of inner plates is one chain link). All KMC 11s chains come with the proprietary "missing link" which, of course, is the half-link of outer plates that join the chain. That brings our count to 117 for KMC. Earlier models of Shimano 11 speed chains came only with a connecting link pin, which has been the Shimano method of joining a chain for 9, 10 and most of 8 speed generations. Beginning again with the newer reiterations of 11s chains having a "QL" in the model name, Shimano developed their proprietary "Quick-link" master link-type joining link which is included with their newer models of 11s chains. Some models are packaged with both a Quick link and link pin included with the chain. So Shimano lengths are 116 or 117 depending on the presence of a Quick link in the package. SRAM 11s chains, both the higher end, Red22, and lower tier, 1130, models are packaged with 114 link chains and their proprietary, "Power-lock" master link for 115 links. Within the 11s chain category are the fully compatible, 11s, e-bike chains. Shimano offers 126 link chains plus Quick link in their e-bike compatible models, CN-601 & 701 QL. One can buy bulk chain and custom cut lengths from that. Probably fairly economical since most chains, however packaged, will require cutting down to size and the associated Quick-links are sold separately in various count configurations as are 11s link pins should one prefer that system.
Because the INNER spacing of chains remain the same for different speed classes of chains, an 11s chain will run on 9s chainrings just fine. The wider spacing between 9s chainrings compared to the rings of 11s cranksets is the source of concern when running a higher speed chain with an overall narrower profile on a crankset designed for a lesser speed drivetrain which has a bit wider spacing between the chainrings. Rougher and slower shifting and the elevated risk of a horribly jammed chain if the narrower 11s chain falls in the wider gaps between 9s chainrings are the big concerns. These types of jams are not of the type where one hops off the bike, takes a finger and lifts the chain out of the gap onto one of the rings. They tend to be severe, very tightly jammed into the gap, and if the chain isn't damaged going in jammed under power, it likely will be by the force required to yank it out. A patient and equipped rider may rectify such a situation by getting lucky with disconnecting the quick link and easing the chain out parallel to the the gap it's jammed in. That's a no go as often as not which then may require loosening or even removing an adjacent chainring's fixing bolts to free the chain. Trying to do this roadside with a multitool's 2-2½" long hex or torx wrench with the crank yet mounted to the bike is tricky at best. You may have the knowledge to know what to do and the prepper foresight to have brought a multi-tool, but you'll surely be challenged figuring out how to get the multitool's flat head screwdriver on the grooves of the inner nut of the chainring bolt at the same time as the hex or torx wrench part of the bolt's outer aspect. If it's coming to all that, the likely reward will be a freed but damaged chain which will now be highly susceptible to derailment and jamming if it can continue to be used at all.
With all that disclaimer out in the open, it is very common to run a front drive of a different speed generation from the rear drive with excellent results. Entirely normal operation can be expected if that difference is one speed generation difference, as in 10s crankset with 9s cassette and chain, or 10s cranks with 11s rear end and chain. It's best, for numerous reasons, to run the correct speed chain as the rear cassette requires, so their will be a degree of mismatch either way up front. Personally, I've run 10 front (2 & 3x) on 9 rear and 11 front (2x) on 10 rear, with flawless performance and quickly dissipating concern for the above risk. A 9s front with 11s rear will work nominally, but I don't feel as though the concern for mid ride problems like above could be brought down to an acceptable level and, given a choice, I would not seek that option for a drivetrain build.