I know it isn't custom level, but you should know about it:
https://scratch.mit.edu/studios/35141809

@CodeScratcherthe1st is right about CustomDB Dev

Ok here’s mine -AKfsgJeyAEAYAoAAAAACqAAAAAA-AAgKgAe4AlAAAAGHAWelco wait your a robot-AKgKgJefAQAYAEAAAAACqAAAAAA-AKf0gJegAOAYAEAAAAACqAAAAAA-AKf/gMegAIASAEAAAAACqAAAAAA-AAgBgAefAOAAAAAAA-AAf9gAefAOAAAAAAA-Alf+f5dqAoAIBuAAAAAAA-AMgTgJeLACAYAkAAAD/D/D/AA-AMfsgJdoAEAYBsAAAD/D/D/AA-AAgNf/exAkAAAAGGAEmployees only area-AXgGf+e9AEACAWAAADFCRANAA-AKf9gVezAiAEAoAAAAACqAAAAAA-AUf/gXdoAsAEBuSYYAA-AAf6gBeQAmAAAAGTASo cool-AfgAgDeNAEAMASAAAD4D4D4AAAA-AfgIgDeUAEAMASGGYD4D4D4AAAA-AfgHgDeDAEAMASGGYD4D4D4AAAA-AfgIgIeLASAEASAAAD4D4D4AAAA-AAgBgAeNApAAAAGHASomeone let me out chompen dude: are you ok?-ABgIgDeKAOAAAAYHYAAABAA-AAf9gAdxAUAAAAAAA-AAgLf/dyAkAAAAGGAVoid trash can! Please do not litter-AMgTgJdPACAYA6AAAD/D/D/AA-AMgTgPd2ACAMAkAAAD/D/D/AA-AMf/gKcyAoAcAEAAAD/D/D/AA-AAfuf3e7AVAAAAGGA-AAgIgNeIAIAAAAAAA-AAf/gBc9AIAAAAAAA-AAfwgBdDARAAAAAAA-AAfygBdDARAAAAAAA-AAf0gBdDARAAAAAAA-AAf1gBdDARAAAAAAA-AAf3gBdDARAAAAAAA-AAf5gBdEARAAAAAAA-AAf7gBdEARAAAAAAA-AAf9gBdEARAAAAAAA-AAf/gBdEARAAAAAAA-AAgBgBdEARAAAAAAA-AAgDgBdEARAAAAAAA-AAgFgBdFARAAAAAAA-AAgHgBdFARAAAAAAA-AAgHgBdFARAAAAAAA-AAgIgBdFARAAAAAAA-AAgKgBdFARAAAAAAA-AAgNgBc9AUAAAAAAA-AAf/gBc9AIAAAAAAA-AAf/gBc9AIAAAAAAA-AAf/gBc9AIAAAAAAA-AAf/gBc9AIAAAAAAA-AAf/gBc9AIAAAAAAA-AAf/gBc9AIAAAAAAA-

Why still use this form? There are so many better alternatives, such as
play db (revival)
custom db (revival a part of pdb now)
robot 64+ (play db mode)
modzone something (I forgot)
robot 64 tag (private server play db level loader v2) [lets you load pdb levels and play them in tag rounds)
TL;DR just use these methods to play levels instead (the best one is probably custom DB)