A bifunctional compound or a stereoisomer or pharmaceutically acceptable salt of Formula X: wherein: the Targeting Ligand is capable of binding to cyclin-dependent kinase 8 and/or cyclin-dependent kinase 19; the Linker is a group that covalently binds to the Targeting Ligand and the Degron; and the Degron is capable of binding to a ubiquitin ligase, wherein the Targeting Ligand is of Formula TL-I: wherein: X is -O-, -NR 5 -, or -Het 2 -; R 5 is H or C 1 -C 6 alkyl; Het 2 is a 3- to 7-membered heterocyclic or a 5-, 8-, or 9-membered heteroaryl ring optionally comprising one or more additional heteroatoms selected from nitrogen, sulfur, and oxygen; u, v, and w together form (i), (ii), or (iii): y and z together form (iv) or (v): Het 1 is heteroaryl comprising one or two 5- or 6-membered rings and 1-4 heteroatoms selected from nitrogen, sulfur, and oxygen, and optionally substituted with NH 2; wherein the Targeting Ligand is bonded to a Linker via the wherein the Degron is of Formula D1: wherein: Y is a bond, (CH 2) 1-6, (CH 2) 0-6 -O, (CH 2) 0-6 -C NR 11, (CH 2) 0-6 -NR 11 C, (CH 2) 0-6 -NH, or (CH 2) 0-6 -NR 12; Z 1 is C or C(R 13) 2; Z 2 is C or C(R 13) 2; R 11 is H or C 1 -C 6 alkyl; R 12 is C 1 -C 6 alkyl or C -C 1 -C 6 alkyl; each R 13 is independently H or C 1 -C 3 alkyl; each R 14 is independently C 1 -C 3 alkyl; R 15 is H, deuterium, C 1 -C 3 alkyl, F, or Cl; each R 16 is independently halogen, OH, C 1 -C 6 alkyl, or C 1 -C 6 alkoxy; q is 0, 1, or 2; and s is 0, 1, 2, or 3, wherein the Degron is covalently bonded to a Linker via the Targeting Ligand is capable of binding to cyclin-dependent kinase 8 and/or cyclin-dependent kinase 19; the Linker is a group that covalently binds to the Targeting Ligand and the Degron; and the Degron is capable of binding to a ubiquitin ligase, wherein the Targeting Ligand is of Formula TL-I: wherein: X is -O-, -NR 5 -, or -Het 2 -; R 5 is H or C 1 -C 6 alkyl; Het 2 is a 3- to 7-membered heterocyclic or a 5-, 8-, or 9-membered heteroaryl ring optionally comprising one or more additional heteroatoms selected from nitrogen, sulfur, and oxygen; u, v, and w together form (i), (ii), or (iii): y and z together form (iv) or (v): Het 1 is heteroaryl comprising one or two 5- or 6-membered rings and 1-4 heteroatoms selected from nitrogen, sulfur, and oxygen, and optionally substituted with NH 2; X is -O-, -NR 5 -, or -Het 2 -; R 5 is H or C 1 -C 6 alkyl; Het 2 is a 3- to 7-membered heterocyclic or a 5-, 8-, or 9-membered heteroaryl ring optionally comprising one or more additional heteroatoms selected from nitrogen, sulfur, and oxygen; u, v, and w together form (i), (ii), or (iii): y and z together form (iv) or (v): Het 1 is heteroaryl comprising one or two 5- or 6-membered rings and 1-4 heteroatoms selected from nitrogen, sulfur, and oxygen, and optionally substituted with NH 2; wherein the Targeting Ligand is bonded to a Linker via the wherein the Degron is of Formula D1: wherein: Y is a bond, (CH 2) 1-6, (CH 2) 0-6 -O, (CH 2) 0-6 -C NR 11, (CH 2) 0-6 -NR 11 C, (CH 2) 0-6 -NH, or (CH 2) 0-6 -NR 12; Z 1 is C or C(R 13) 2; Z 2 is C or C(R 13) 2; R 11 is H or C 1 -C 6 alkyl; R 12 is C 1 -C 6 alkyl or C -C 1 -C 6 alkyl; each R 13 is independently H or C 1 -C 3 alkyl; each R 14 is independently C 1 -C 3 alkyl; R 15 is H, deuterium, C 1 -C 3 alkyl, F, or Cl; each R 16 is independently halogen, OH, C 1 -C 6 alkyl, or C 1 -C 6 alkoxy; q is 0, 1, or 2; and s is 0, 1, 2, or 3, wherein the Degron is covalently bonded to a Linker via Y is a bond, (CH 2) 1-6, (CH 2) 0-6 -O, (CH 2) 0-6 -C NR 11, (CH 2) 0-6 -NR 11 C, (CH 2) 0-6 -NH, or (CH 2) 0-6 -NR 12; Z 1 is C or C(R 13) 2; Z 2 is C or C(R 13) 2; R 11 is H or C 1 -C 6 alkyl; R 12 is C 1 -C 6 alkyl or C -C 1 -C 6 alkyl; each R 13 is independently H or C 1 -C 3 alkyl; each R 14 is independently C 1 -C 3 alkyl; R 15 is H, deuterium, C 1 -C 3 alkyl, F, or Cl; each R 16 is independently halogen, OH, C 1 -C 6 alkyl, or C 1 -C 6 alkoxy; q is 0, 1, or 2; and s is 0, 1, 2, or 3, wherein the Degron is covalently bonded to a Linker via