Lenders don’t use the score you see on your credit file. This is a number the Credit Reference Agency makes up to sell you services which aim to help you (pointlessly) curate your score with them.
Lenders look at things such as your borrowing history, debt to income ratio, debt to credit limit ratio, affordability, ability to pay debt back on time and pay more than minimum amounts, and, I’m afraid, frequency of applications for credit as this can seem to be an indicator of desperation for credit and bad money management.
Lenders then apply their own, secret, scores to these criteria and see if you fit their target market. This is why you’ll see some companies happy to lend to people they see as poor risk, and others not.
Monzo would take an individual decision as to whether they thought you’d attempted to apply for too much credit, and would, in the process add another check to the pile, which in turn might influence other lenders. But no one knows how each lender assesses potential borrowers, so no one, including the Credit Reference Agencies will be able to say if this will prevent/enhance your chance to get credit in the future.
So by all means apply for another limit with Monzo, but keep in the back of your mind how multiple applications can look to certain lenders in the eco system of your credit history file, which the Credit Reference Agencies provide. If you begin to get rejected, stop applying for a while and try to pay down your debt.
Hope that helps?