Some help please

Well you could certainly make the upgrade to get to a articulating flip screen. I don't think you will feel much of a difference for the investment otherwise. You may get an extra feature or two, and a slight boost in megapixels, frames per second or ISO noise performance depending on what model you currently own.
lets talk the models above a second:

• The M50, one of 11 M lineup cameras. The M mount is canons first entry into mirror-less starting in 2012, these cameras rely on the live view of the sensor to display the image just like your point and shoot cameras, except they have apc sized sensors like your entry level dslrs and you can change lenses. There are only 8 EF-M mount lens from canon. These are light and probably a good choice for vlogging at a reasonable price point. I would also note that the Canon RF mount made for their higher end new series of full frame mirror-less is likely the future and I see them phasing out the M lineup since canon has only made 8 m lenses in 8 years.
  
• The 77D, this is a mid step between the 800d and 80d cameras it adopts features from both while finding a price point that some will find attractive. Canon has really stretched out the steps in the ladder that is their lineup over the years. I would really consider this closer to the 800d than the 80d personally. I can try to summarize the lineup at a high level and you can get an idea where the camera falls in:
  • To keep it simple the Rebels are the more intro/enthusiast level ones which are more automatic and less customizable, they are also more plastic in their build. These have two obvious tiers in naming/features and pricing, depending on country it goes from 4digit to 3 digit numbers or in us for example rebel t7 to t7i.
    
  • The Middle tier is the two digit tier and the advanced armature/enthusiast level. These are more rugged built bodies usually with some weather sealing, have extra dials and LCD screens and allow much more customization. You will see a noticeable bump in performance. The numbering is like 70d 80d or 90d for example.
    
  • All these cameras use similar APC sized sensors, the DSLRs take crop lenses EF-S as well as standard EF lenses.
  • The 3rd tier is the higher end cameras, these are your single digit series cameras, many of these are full frame sensor cameras and if you have a full frame you need to use the EF lenses.

At this link you can see a table at the bottom that shows the lineup and how it went from 3 primary tiers to a number of partial smaller steps in the lineup: https://en.wikipedia.org/wiki/Comparison_of_Canon_EOS_digital_cameras

 

Followup question besides a flip screen what else are you looking to get from your investment, or where do you feel your camera falls short?
Typically I recommend buying better lenses before upgrading cameras, this is where the images really are made.
Also my initial reaction to upgrading your lets say t6 which was what i guessed you have may be better holding out till you can afford a 90d on sale, so you get the most out of an upgrade.

 

That is helpful, if your looking to make the switch, stay in a similar tier of camera, have the swivel touch screen and an audio jack i think I would recommend the 77d. That is given you price range that would be my recommendation. I still think the 90d is a much better jump in camera but it is a bit out of the price range you are looking at.
The short answer to why I would pick 77d over the 7ti which is similar in many specs, well it has the additional top LCD and the second control dial on the back like the bigger brothers in the canon lineup. These both aid in changing setting quickly and on the fly without relying on the touch screen. I don't believe your d3500 had either similar to the t7/t7i bodies. After having them I can't imagine giving them up, so I would highly recommend jumping up to the ergonomics of the middle and upper tier since you have the chance.