Ah... you have thrown the perfect tool for this job out. What is left is to turn on bandwidth limiting and hi-res mode to get a cleaner signal.
I know. I’m not impressed with my quick decision. At all.
I have the bandwidth limit on and eres didn’t do anything to make the dc signal pop out any better.
I don’t know what else to try on this scope. Wishing I wouldn’t have chosen between the two so quickly.
Of course there is different scopes and different methods to filter out higher frequencies. Some scopes, like example GW have user settable low pass, band pass and high pass filters and quite useful in some situations but not all. Also some older Siglent have these. But then it need also note that these are made in digital side (DSP). In some cases, my opinion is that even they works ok many times but - as told they are digital side. If example low pass filter freq is set for 100kHz how it know if signal is true signal or false signal produced internally before this digital filter.
So or so, I do not want start infinite unnecessary debate about this.
If you really have there high noise level in signals, in signal itself and more due to noisy environment and noisy ground and ground loops.
You can - if you have available - differential probe.
But if there is still in signal line itself high noise...
If you have some materials and tools... and can do some experimental things.
You can filter noise out _before_ scope input.
Because I do not know enough details about your signals under tesdt and what you need look, exmple what kind of risetimes/frequencies you need look and what are these what can filter out.
Because I do not know your signal true level related to ground I can not recommend next.
Set probe to 1x (and scope). Take 1kohm resistor. Other end to probe tip and other end to signal. Then connect 0.1uF capacitor from probe tip to probe ground (just this ground what is around 5mm after tip. (take this hook out first). Then look how it looks now. After then, depending result, can think more.
(this is 1kHz 1st order LPF what give 20dB attenuation for decade. It is not lot but it may give some idea what to next. You can do same with cheap 50ohm or 75 ohm coaxial.
Because, what ever skope yuu take if there is very heavy noise and it go to scope front end and to ADC it may still rotten your result. So it is some cases quite wise use filter before scope input.
Your connection to signal in one image looks really poor. It is like "please come in all noise..please come all in... "
Also your probe... (in image I can see setup with 10x) it is full band in 10x
Scope input 20M BW is also something like 1st order filter sxo even it do not attenuate even 40 - 100MHz very well.
But this same probe in 1x mode, it acts also like 1st order LPF around 5 - 8MHz, together with 20M BW you have bit bnetter attenuation but 0 - several MHz come in without attenuation. Do you need look 10MHz or 35ns risetimes. I think not...
It do not cost lot if you make some trial with simple external RC (but also this, do it so that it also attenuate and is not like antenna for collecting all noise.
I think whole problem is "how to connect this signal to scope" (and how to filter it before scope input)
There is no scope what have internal analog side low frequency low pass settable filters. Least I do not know any - and over 50 years have not seen any. But very often have used external filters before oscilloscope inout and in some cases they are really easy to do (exept if need more steep that 2nd order)
You can start with one resistor and one capacitor. After then
if it looks anyhow useful you can think how to do it bit more better and usable. Test do not cost nearly anything. Just think what are highest frequencies/fastest risetimes what you need see reliable without attenuation... this is starting point.