Question
Anything wrong with connecting L298Ns in parallel?
Answer
Nothing wrong. Hobbyists do it. Engineers can also do it. It all depends on cost/benefit/risk hobbyist/engineer trade offs.
Let me explain, starting with ULN2803, then L298N.
Part A - ULN2803A Case
ULN2803A Darlington Transistor Arrays - TI
From datasheet - Section 3 Description
The ULN2803A device is a 50V, 500 mA Darlington transistor array. The device consists of eight NPN Darlington pairs that feature high-voltage outputs with common-cathode clamp diodes for switching inductive loads. The collector-current rating of each Darlington pair is 500 mA.
The Darlington pairs may be connected in parallel for higher current capability.
Part B - L298N Case
By the same ULN2803 token, L298N can also parallel output for bigger current. Since the BJTs to be paralleled are fabricated from the same die/chip, they should very nicely selfie balancing out the load current.
Part 3 - L298N Dual Full Bride DC Motor Driver Module Case
AliExpress L298N Dual Full H Bridge DC Motor Driver Module - US$1
The very popular cheapy L298N motor driver modules are for driving two 4A DC motors. For a bigger motor, say 8A, we can parallel two drivers into one big driver.
Warning: me just friendly hobbyist. No guarantee no nothing would melt down or blow up.
Part 4 - Discussion and Recommendation
L298N output paralleling for bigger output current is a good newbie workaround. For ninjas, I would recommend forgetting the little old guy L298N, and go instead for the 40A big guy BTN7971B.
For more details on BTN7971B, see Refs 11.4, 11.5, and 11.6 of my answer to the following motor driver Q&A.