There's a YouTube limit of 75 maximum new subscriptions on your YouTube / YouTube Music account per day (24 hours).
Also, there's a limit of channels / artists you can subscribe to in total. It's not an exact limit:
"In general, you can subscribe to a maximum of 2,000 channels. However, your subscription limit grows as your YouTube channel does — it's tied to the number of subscribers your channel has or how long your account has existed, so your exact limits may change over time.
We recommend capping your account to 5,000 channel subscriptions to make sure the subscriptions feed and channel list give the best experience."