You are limited to what Apple used for CPU’s. Your system is limited to these [https://everymac.com/ultimate-mac-lookup/?search_keywords=iMac19,2|iMac19,2]
The highest performing CPU your system can support is [https://ark.intel.com/content/www/us/en/ark/products/126686/intel-core-i7-8700-processor-12m-cache-up-to-4-60-ghz.html|3.2 GHz Core i7 (I7-8700)] CPU
Between the limits in the systems firmware as well as the systems cooling and its power it will not support the [https://ark.intel.com/content/www/us/en/ark/products/191044/intel-core-i9-9900t-processor-16m-cache-up-to-4-40-ghz.html|4.40 GHz Core i9 (I9 9900T)] CPU