Your requirements and the exact phrasing is what makes this difficult, if not impossible to answer. If I follow your request to the letter, you want something that does PPPoE at 1 GBit/s line speed (that is already not trivial to do, without a survey of rather different hardware, combined with adguard home (this is easier, in regards to the base load - but harder to answer when it comes to really large blocklists or advanced filtering rules, so quite some variance between minimal, expectable-median and worst case situations). iperf is useless for the router itself, but drives up the requirements considerably - and "Some free power to run some more software in case it's needed" is completely impossible to evaluate in terms of CPU/ storage and RAM needs.
So you come up with a very fuzzy/ vague list of requirements (might be obvious to you, but isn't for anyone else), while at the same time with a massive variance between minimum, expected median and maximum system requirements. But at the same time you're requesting an exact specification for the minimum system requirements, with no margin for overshooting this - that's simply not possible.
So you have 500Mbps-1Gbps fiber and need a router READ THIS FIRST is still valid, some N100 based x86_64 system with four 2.5GBASE-T ports does meet your listed requirements, but it does overshoot your target performance - still, around 120-230 EUR, plus switch(es) and AP(s) is a very reasonable choice for your situation, leaving substantial margins.
Would filogic 820/ 830/ 880 meet these requirements? Perhaps, but it does rely on hardware flow-offloading for this, which is a little fragile, especially in combination with PPPoE and it might be marginal for iperf3 on the device and "Some free power to run some more software in case it's needed".
Would one of the newer rockchip based NanoPi meet them? Quite probably, but with fewer onboard ethernet ports and the same requirements for external switches and APs - but especially the newer ones are still waiting to be fully supported. The same goes for the RPi4/ RPi5, with the additional complication of those needing a USB3 ethernet card on top.
Would ipq807x meet the bar? Very likely not, not with PPPoE and without NSS acceleration.
What about mt7622? Similar situation as filogic 820/ 830, but with less SOC performance - it may be just enough, but with your fuzzy additional requirements and seeing it slowly disappear from the market (in favour of mt7621a+mt7915DBDC on the low-end and filogic 820/ 830 on the mid- to high-end), this wouldn't be my first pick right now.