Based from YouTuber reviews, the Ryzen 5 3600 (non X and non XT), kaya niya ma-pair with the RTX 2080Ti without bottlenecking of any kind. Since 6-core, 12-threads, kaya pa niya mag game and stream at the same time. (I don't know what your application is but yeah)
Pag nag 4000 series CPUs ka, di ka 100% sure na compatible ang mga B450 motherboards (some Motherboards manufacturers might still update the older board's BIOS some may not), so mapipilitan ka mag B550 or X570 which is way more expensive and for me, ang only real benefit is the option for PCIE 4.0 which is basically useless unless bibili ka ng PCIE 4.0 na SSD na sobrang mahal (Pero sobra ding bilis). Di naman daw namamaximize ng mga current GPU's ang PCIE 3.0. (kahit ng Titan RTX)
AMD's 4000 series is the last generation of CPUs to use the AM4 socket, according to AMD. nakaka 5 years of support na daw kasi. So, after nitong release which is expected by Q4 2020, bago nanaman ang socket, so palit pati MOBO and maybe even PSU? if mag uupgrade ka after that.
Para sakin sir, if you dont really need PCIE 4.0, stay put nalang muna sa 3000 series and B450 motherboards. Unless you're working on CPU intensive workloads, I'd say ok na ang R5 3600. It is btw, the best all-around CPU.